diff --git a/third_party/WebKit/Source/core/dom/Document.cpp b/third_party/WebKit/Source/core/dom/Document.cpp
index da5e6752a16732..16c6f1902d77b9 100644
--- a/third_party/WebKit/Source/core/dom/Document.cpp
+++ b/third_party/WebKit/Source/core/dom/Document.cpp
@@ -3542,7 +3542,7 @@ ReferrerPolicy Document::getReferrerPolicy() const {
 MouseEventWithHitTestResults Document::performMouseEventHitTest(
     const HitTestRequest& request,
     const LayoutPoint& documentPoint,
-    const PlatformMouseEvent& event) {
+    const WebMouseEvent& event) {
   DCHECK(layoutViewItem().isNull() || layoutViewItem().isLayoutView());
 
   // LayoutView::hitTest causes a layout, and we don't want to hit that until
@@ -3562,15 +3562,13 @@ MouseEventWithHitTestResults Document::performMouseEventHitTest(
     updateHoverActiveState(request, result.innerElement(), result.scrollbar());
 
   if (isHTMLCanvasElement(result.innerNode())) {
-    PlatformMouseEvent eventWithRegion = event;
     HitTestCanvasResult* hitTestCanvasResult =
         toHTMLCanvasElement(result.innerNode())
             ->getControlAndIdIfHitRegionExists(result.pointInInnerNodeFrame());
     if (hitTestCanvasResult->getControl()) {
       result.setInnerNode(hitTestCanvasResult->getControl());
     }
-    eventWithRegion.setRegion(hitTestCanvasResult->getId());
-    return MouseEventWithHitTestResults(eventWithRegion, result);
+    result.setCanvasRegionId(hitTestCanvasResult->getId());
   }
 
   return MouseEventWithHitTestResults(event, result);
diff --git a/third_party/WebKit/Source/core/dom/Document.h b/third_party/WebKit/Source/core/dom/Document.h
index a46b828b0d4250..746f7f59f8d1f3 100644
--- a/third_party/WebKit/Source/core/dom/Document.h
+++ b/third_party/WebKit/Source/core/dom/Document.h
@@ -141,7 +141,6 @@ class NodeIterator;
 class NthIndexCache;
 class OriginAccessEntry;
 class Page;
-class PlatformMouseEvent;
 class ProcessingInstruction;
 class PropertyRegistry;
 class QualifiedName;
@@ -172,12 +171,12 @@ class TouchList;
 class TransformSource;
 class TreeWalker;
 class VisitedLinkState;
+class WebMouseEvent;
 struct AnnotatedRegionValue;
 struct FocusParams;
 struct IconURL;
 
-using MouseEventWithHitTestResults =
-    EventWithHitTestResults<PlatformMouseEvent>;
+using MouseEventWithHitTestResults = EventWithHitTestResults<WebMouseEvent>;
 using ExceptionCode = int;
 
 enum NodeListInvalidationType {
@@ -687,10 +686,9 @@ class CORE_EXPORT Document : public ContainerNode,
   TextLinkColors& textLinkColors() { return m_textLinkColors; }
   VisitedLinkState& visitedLinkState() const { return *m_visitedLinkState; }
 
-  MouseEventWithHitTestResults performMouseEventHitTest(
-      const HitTestRequest&,
-      const LayoutPoint&,
-      const PlatformMouseEvent&);
+  MouseEventWithHitTestResults performMouseEventHitTest(const HitTestRequest&,
+                                                        const LayoutPoint&,
+                                                        const WebMouseEvent&);
 
   /* Newly proposed CSS3 mechanism for selecting alternate
        stylesheets using the DOM. May be subject to change as
diff --git a/third_party/WebKit/Source/core/dom/Node.cpp b/third_party/WebKit/Source/core/dom/Node.cpp
index 66fb351cd033a4..0c491557b80f31 100644
--- a/third_party/WebKit/Source/core/dom/Node.cpp
+++ b/third_party/WebKit/Source/core/dom/Node.cpp
@@ -2119,7 +2119,7 @@ DispatchEventResult Node::dispatchDOMActivateEvent(int detail,
 }
 
 void Node::createAndDispatchPointerEvent(const AtomicString& mouseEventName,
-                                         const PlatformMouseEvent& mouseEvent,
+                                         const WebMouseEvent& mouseEvent,
                                          LocalDOMWindow* view) {
   AtomicString pointerEventName;
   if (mouseEventName == EventTypeNames::mousemove)
@@ -2137,22 +2137,22 @@ void Node::createAndDispatchPointerEvent(const AtomicString& mouseEventName,
   pointerEventInit.setPointerType("mouse");
   pointerEventInit.setIsPrimary(true);
   pointerEventInit.setButtons(
-      MouseEvent::platformModifiersToButtons(mouseEvent.getModifiers()));
+      MouseEvent::platformModifiersToButtons(mouseEvent.modifiers()));
 
   pointerEventInit.setBubbles(true);
   pointerEventInit.setCancelable(true);
   pointerEventInit.setComposed(true);
   pointerEventInit.setDetail(0);
 
-  pointerEventInit.setScreenX(mouseEvent.globalPosition().x());
-  pointerEventInit.setScreenY(mouseEvent.globalPosition().y());
+  pointerEventInit.setScreenX(mouseEvent.globalX);
+  pointerEventInit.setScreenY(mouseEvent.globalY);
 
   IntPoint locationInFrameZoomed;
   if (view && view->frame() && view->frame()->view()) {
     LocalFrame* frame = view->frame();
     FrameView* frameView = frame->view();
-    IntPoint locationInContents =
-        frameView->rootFrameToContents(mouseEvent.position());
+    IntPoint locationInContents = frameView->rootFrameToContents(
+        flooredIntPoint(mouseEvent.positionInRootFrame()));
     locationInFrameZoomed = frameView->contentsToFrame(locationInContents);
     float scaleFactor = 1 / frame->pageZoomFactor();
     locationInFrameZoomed.scale(scaleFactor, scaleFactor);
@@ -2164,28 +2164,30 @@ void Node::createAndDispatchPointerEvent(const AtomicString& mouseEventName,
 
   if (pointerEventName == EventTypeNames::pointerdown ||
       pointerEventName == EventTypeNames::pointerup) {
-    pointerEventInit.setButton(
-        static_cast<int>(mouseEvent.pointerProperties().button));
+    pointerEventInit.setButton(static_cast<int>(mouseEvent.button));
   } else {
     pointerEventInit.setButton(
         static_cast<int>(WebPointerProperties::Button::NoButton));
   }
 
-  UIEventWithKeyState::setFromPlatformModifiers(pointerEventInit,
-                                                mouseEvent.getModifiers());
+  UIEventWithKeyState::setFromWebInputEventModifiers(
+      pointerEventInit,
+      static_cast<WebInputEvent::Modifiers>(mouseEvent.modifiers()));
   pointerEventInit.setView(view);
 
   dispatchEvent(PointerEvent::create(pointerEventName, pointerEventInit));
 }
 
-void Node::dispatchMouseEvent(const PlatformMouseEvent& nativeEvent,
+void Node::dispatchMouseEvent(const WebMouseEvent& nativeEvent,
                               const AtomicString& mouseEventType,
                               int detail,
+                              const String& canvasRegionId,
                               Node* relatedTarget) {
   createAndDispatchPointerEvent(mouseEventType, nativeEvent,
                                 document().domWindow());
   dispatchEvent(MouseEvent::create(mouseEventType, document().domWindow(),
-                                   nativeEvent, detail, relatedTarget));
+                                   nativeEvent, detail, canvasRegionId,
+                                   relatedTarget));
 }
 
 void Node::dispatchSimulatedClick(Event* underlyingEvent,
diff --git a/third_party/WebKit/Source/core/dom/Node.h b/third_party/WebKit/Source/core/dom/Node.h
index c02e8527d0a984..48f16d982ecc79 100644
--- a/third_party/WebKit/Source/core/dom/Node.h
+++ b/third_party/WebKit/Source/core/dom/Node.h
@@ -60,7 +60,6 @@ class EventDispatchHandlingState;
 class NodeList;
 class NodeListsNodeData;
 class NodeRareData;
-class PlatformMouseEvent;
 class QualifiedName;
 class RegisteredEventListener;
 class LayoutBox;
@@ -74,6 +73,7 @@ class StaticNodeTypeList;
 using StaticNodeList = StaticNodeTypeList<Node>;
 class StyleChangeReasonForTracing;
 class Text;
+class WebMouseEvent;
 
 const int nodeStyleChangeShift = 18;
 const int nodeCustomElementShift = 20;
@@ -717,9 +717,10 @@ class CORE_EXPORT Node : public EventTarget {
   DispatchEventResult dispatchDOMActivateEvent(int detail,
                                                Event& underlyingEvent);
 
-  void dispatchMouseEvent(const PlatformMouseEvent&,
+  void dispatchMouseEvent(const WebMouseEvent&,
                           const AtomicString& eventType,
                           int clickCount = 0,
+                          const String& canvasNodeId = String(),
                           Node* relatedTarget = nullptr);
 
   void dispatchSimulatedClick(
@@ -842,10 +843,10 @@ class CORE_EXPORT Node : public EventTarget {
   void clearFlag(NodeFlags mask) { m_nodeFlags &= ~mask; }
 
   // TODO(mustaq): This is a hack to fix sites with flash objects. We should
-  // instead route all PlatformMouseEvents through EventHandler. See
+  // instead route all WebMouseEvents through EventHandler. See
   // crbug.com/665924.
   void createAndDispatchPointerEvent(const AtomicString& mouseEventName,
-                                     const PlatformMouseEvent&,
+                                     const WebMouseEvent&,
                                      LocalDOMWindow* view);
 
  protected:
diff --git a/third_party/WebKit/Source/core/editing/SelectionController.cpp b/third_party/WebKit/Source/core/editing/SelectionController.cpp
index 390e6def00fd5f..b798e6497b6c6e 100644
--- a/third_party/WebKit/Source/core/editing/SelectionController.cpp
+++ b/third_party/WebKit/Source/core/editing/SelectionController.cpp
@@ -180,8 +180,8 @@ bool SelectionController::handleMousePressEventSingleClick(
   // Don't restart the selection when the mouse is pressed on an
   // existing selection so we can allow for text dragging.
   if (FrameView* view = m_frame->view()) {
-    const LayoutPoint vPoint =
-        view->rootFrameToContents(event.event().position());
+    const LayoutPoint vPoint = view->rootFrameToContents(
+        flooredIntPoint(event.event().positionInRootFrame()));
     if (!extendSelection && this->selection().contains(vPoint)) {
       m_mouseDownWasSingleClickInSelection = true;
       if (!event.event().fromTouch())
@@ -245,8 +245,8 @@ bool SelectionController::handleMousePressEventSingleClick(
                                    .selectAllChildren(*innerNode)
                                    .build())
             .isCaret();
-    const bool notLeftClick = event.event().pointerProperties().button !=
-                              WebPointerProperties::Button::Left;
+    const bool notLeftClick =
+        event.event().button != WebPointerProperties::Button::Left;
     if (!isTextBoxEmpty || notLeftClick)
       isHandleVisible = event.event().fromTouch();
   }
@@ -538,7 +538,7 @@ void SelectionController::selectClosestWordFromMouseEvent(
     return;
 
   AppendTrailingWhitespace appendTrailingWhitespace =
-      (result.event().clickCount() == 2 &&
+      (result.event().clickCount == 2 &&
        m_frame->editor().isSelectTrailingWhitespaceEnabled())
           ? AppendTrailingWhitespace::ShouldAppend
           : AppendTrailingWhitespace::DontAppend;
@@ -558,7 +558,7 @@ void SelectionController::selectClosestMisspellingFromMouseEvent(
 
   selectClosestMisspellingFromHitTestResult(
       result.hitTestResult(),
-      (result.event().clickCount() == 2 &&
+      (result.event().clickCount == 2 &&
        m_frame->editor().isSelectTrailingWhitespaceEnabled())
           ? AppendTrailingWhitespace::ShouldAppend
           : AppendTrailingWhitespace::DontAppend);
@@ -733,8 +733,7 @@ bool SelectionController::handleMousePressEventDoubleClick(
   if (!m_mouseDownAllowsMultiClick)
     return handleMousePressEventSingleClick(event);
 
-  if (event.event().pointerProperties().button !=
-      WebPointerProperties::Button::Left)
+  if (event.event().button != WebPointerProperties::Button::Left)
     return false;
 
   if (selection().isRange()) {
@@ -763,8 +762,7 @@ bool SelectionController::handleMousePressEventTripleClick(
   if (!m_mouseDownAllowsMultiClick)
     return handleMousePressEventSingleClick(event);
 
-  if (event.event().pointerProperties().button !=
-      WebPointerProperties::Button::Left)
+  if (event.event().button != WebPointerProperties::Button::Left)
     return false;
 
   Node* innerNode = event.innerNode();
@@ -865,9 +863,9 @@ bool SelectionController::handleMouseReleaseEvent(
   // editing, place the caret.
   if (m_mouseDownWasSingleClickInSelection &&
       m_selectionState != SelectionState::ExtendedSelection &&
-      dragStartPos == event.event().position() && selection().isRange() &&
-      event.event().pointerProperties().button !=
-          WebPointerProperties::Button::Right) {
+      dragStartPos == flooredIntPoint(event.event().positionInRootFrame()) &&
+      selection().isRange() &&
+      event.event().button != WebPointerProperties::Button::Right) {
     // TODO(xiaochengh): The use of updateStyleAndLayoutIgnorePendingStylesheets
     // needs to be audited.  See http://crbug.com/590369 for more details.
     m_frame->document()->updateStyleAndLayoutIgnorePendingStylesheets();
@@ -893,8 +891,7 @@ bool SelectionController::handleMouseReleaseEvent(
 
   selection().selectFrameElementInParentIfFullySelected();
 
-  if (event.event().pointerProperties().button ==
-          WebPointerProperties::Button::Middle &&
+  if (event.event().button == WebPointerProperties::Button::Middle &&
       !event.isOverLink()) {
     // Ignore handled, since we want to paste to where the caret was placed
     // anyway.
@@ -905,7 +902,7 @@ bool SelectionController::handleMouseReleaseEvent(
 }
 
 bool SelectionController::handlePasteGlobalSelection(
-    const PlatformMouseEvent& mouseEvent) {
+    const WebMouseEvent& mouseEvent) {
   // If the event was a middle click, attempt to copy global selection in after
   // the newly set caret position.
   //
@@ -922,7 +919,7 @@ bool SelectionController::handlePasteGlobalSelection(
   // down then the text is pasted just before the onclick handler runs and
   // clears the text box. So it's important this happens after the event
   // handlers have been fired.
-  if (mouseEvent.type() != PlatformEvent::MouseReleased)
+  if (mouseEvent.type() != WebInputEvent::MouseUp)
     return false;
 
   if (!m_frame->page())
@@ -1022,7 +1019,8 @@ void SelectionController::passMousePressEventToSubframe(
   // greyed out even though we're clicking on the selection.  This looks
   // really strange (having the whole frame be greyed out), so we deselect the
   // selection.
-  IntPoint p = m_frame->view()->rootFrameToContents(mev.event().position());
+  IntPoint p = m_frame->view()->rootFrameToContents(
+      flooredIntPoint(mev.event().positionInRootFrame()));
   if (!selection().contains(p))
     return;
 
@@ -1071,13 +1069,16 @@ FrameSelection& SelectionController::selection() const {
 }
 
 bool isLinkSelection(const MouseEventWithHitTestResults& event) {
-  return event.event().altKey() && event.isOverLink();
+  return (event.event().modifiers() & WebInputEvent::Modifiers::AltKey) != 0 &&
+         event.isOverLink();
 }
 
 bool isExtendingSelection(const MouseEventWithHitTestResults& event) {
   bool isMouseDownOnLinkOrImage =
       event.isOverLink() || event.hitTestResult().image();
-  return event.event().shiftKey() && !isMouseDownOnLinkOrImage;
+  return (event.event().modifiers() & WebInputEvent::Modifiers::ShiftKey) !=
+             0 &&
+         !isMouseDownOnLinkOrImage;
 }
 
 }  // namespace blink
diff --git a/third_party/WebKit/Source/core/editing/SelectionController.h b/third_party/WebKit/Source/core/editing/SelectionController.h
index 8d847cca22f637..69abbddcbbe724 100644
--- a/third_party/WebKit/Source/core/editing/SelectionController.h
+++ b/third_party/WebKit/Source/core/editing/SelectionController.h
@@ -62,7 +62,7 @@ class CORE_EXPORT SelectionController final
                                const IntPoint&);
   bool handleMouseReleaseEvent(const MouseEventWithHitTestResults&,
                                const LayoutPoint&);
-  bool handlePasteGlobalSelection(const PlatformMouseEvent&);
+  bool handlePasteGlobalSelection(const WebMouseEvent&);
   bool handleGestureLongPress(const WebGestureEvent&, const HitTestResult&);
   void handleGestureTwoFingerTap(const GestureEventWithHitTestResults&);
   void handleGestureLongTap(const GestureEventWithHitTestResults&);
diff --git a/third_party/WebKit/Source/core/events/DragEvent.cpp b/third_party/WebKit/Source/core/events/DragEvent.cpp
index 61e44d418bf851..9512e6cd8dceab 100644
--- a/third_party/WebKit/Source/core/events/DragEvent.cpp
+++ b/third_party/WebKit/Source/core/events/DragEvent.cpp
@@ -10,25 +10,24 @@
 
 namespace blink {
 
-DragEvent* DragEvent::create(
-    const AtomicString& type,
-    bool canBubble,
-    bool cancelable,
-    AbstractView* view,
-    int detail,
-    int screenX,
-    int screenY,
-    int windowX,
-    int windowY,
-    int movementX,
-    int movementY,
-    PlatformEvent::Modifiers modifiers,
-    short button,
-    unsigned short buttons,
-    EventTarget* relatedTarget,
-    TimeTicks platformTimeStamp,
-    DataTransfer* dataTransfer,
-    PlatformMouseEvent::SyntheticEventType syntheticEventType) {
+DragEvent* DragEvent::create(const AtomicString& type,
+                             bool canBubble,
+                             bool cancelable,
+                             AbstractView* view,
+                             int detail,
+                             int screenX,
+                             int screenY,
+                             int windowX,
+                             int windowY,
+                             int movementX,
+                             int movementY,
+                             PlatformEvent::Modifiers modifiers,
+                             short button,
+                             unsigned short buttons,
+                             EventTarget* relatedTarget,
+                             TimeTicks platformTimeStamp,
+                             DataTransfer* dataTransfer,
+                             SyntheticEventType syntheticEventType) {
   return new DragEvent(type, canBubble, cancelable, view, detail, screenX,
                        screenY, windowX, windowY, movementX, movementY,
                        modifiers, button, buttons, relatedTarget,
@@ -57,7 +56,7 @@ DragEvent::DragEvent(const AtomicString& eventType,
                      EventTarget* relatedTarget,
                      TimeTicks platformTimeStamp,
                      DataTransfer* dataTransfer,
-                     PlatformMouseEvent::SyntheticEventType syntheticEventType)
+                     SyntheticEventType syntheticEventType)
     : MouseEvent(
           eventType,
           canBubble,
@@ -78,8 +77,7 @@ DragEvent::DragEvent(const AtomicString& eventType,
           syntheticEventType,
           // TODO(zino): Should support canvas hit region because the drag event
           // is a kind of mouse event. Please see http://crbug.com/594073
-          String(),
-          nullptr),
+          String()),
       m_dataTransfer(dataTransfer)
 
 {}
diff --git a/third_party/WebKit/Source/core/events/DragEvent.h b/third_party/WebKit/Source/core/events/DragEvent.h
index e1d6fcb85864b3..2bdef6ef886856 100644
--- a/third_party/WebKit/Source/core/events/DragEvent.h
+++ b/third_party/WebKit/Source/core/events/DragEvent.h
@@ -40,8 +40,7 @@ class CORE_EXPORT DragEvent final : public MouseEvent {
                            EventTarget* relatedTarget,
                            TimeTicks platformTimeStamp,
                            DataTransfer*,
-                           PlatformMouseEvent::SyntheticEventType =
-                               PlatformMouseEvent::RealOrIndistinguishable);
+                           SyntheticEventType = RealOrIndistinguishable);
 
   static DragEvent* create(const AtomicString& type,
                            const DragEventInit& initializer) {
@@ -79,7 +78,7 @@ class CORE_EXPORT DragEvent final : public MouseEvent {
             EventTarget* relatedTarget,
             TimeTicks platformTimeStamp,
             DataTransfer*,
-            PlatformMouseEvent::SyntheticEventType);
+            SyntheticEventType);
 
   DragEvent(const AtomicString& type, const DragEventInit&);
 
diff --git a/third_party/WebKit/Source/core/events/MouseEvent.cpp b/third_party/WebKit/Source/core/events/MouseEvent.cpp
index da7a86940579ba..5e68f976bc08bc 100644
--- a/third_party/WebKit/Source/core/events/MouseEvent.cpp
+++ b/third_party/WebKit/Source/core/events/MouseEvent.cpp
@@ -32,7 +32,6 @@
 #include "core/layout/LayoutObject.h"
 #include "core/paint/PaintLayer.h"
 #include "core/svg/SVGElement.h"
-#include "platform/PlatformMouseEvent.h"
 #include "public/platform/WebPointerProperties.h"
 
 namespace blink {
@@ -91,48 +90,16 @@ MouseEvent* MouseEvent::create(ScriptState* scriptState,
 
 MouseEvent* MouseEvent::create(const AtomicString& eventType,
                                AbstractView* view,
-                               const PlatformMouseEvent& event,
+                               const WebMouseEvent& event,
                                int detail,
+                               const String& canvasRegionId,
                                Node* relatedTarget) {
   bool isMouseEnterOrLeave = eventType == EventTypeNames::mouseenter ||
                              eventType == EventTypeNames::mouseleave;
   bool isCancelable = !isMouseEnterOrLeave;
   bool isBubbling = !isMouseEnterOrLeave;
-
-  return MouseEvent::create(
-      eventType, isBubbling, isCancelable, view, detail,
-      event.globalPosition().x(), event.globalPosition().y(),
-      event.position().x(), event.position().y(), event.movementDelta().x(),
-      event.movementDelta().y(), event.getModifiers(),
-      static_cast<short>(event.pointerProperties().button),
-      platformModifiersToButtons(event.getModifiers()), relatedTarget,
-      event.timestamp(), event.getSyntheticEventType(), event.region(), &event);
-}
-
-MouseEvent* MouseEvent::create(
-    const AtomicString& type,
-    bool canBubble,
-    bool cancelable,
-    AbstractView* view,
-    int detail,
-    int screenX,
-    int screenY,
-    int windowX,
-    int windowY,
-    int movementX,
-    int movementY,
-    PlatformEvent::Modifiers modifiers,
-    short button,
-    unsigned short buttons,
-    EventTarget* relatedTarget,
-    TimeTicks platformTimeStamp,
-    PlatformMouseEvent::SyntheticEventType syntheticEventType,
-    const String& region,
-    const PlatformMouseEvent* mouseEvent) {
-  return new MouseEvent(
-      type, canBubble, cancelable, view, detail, screenX, screenY, windowX,
-      windowY, movementX, movementY, modifiers, button, buttons, relatedTarget,
-      platformTimeStamp, syntheticEventType, region, mouseEvent);
+  return new MouseEvent(eventType, isBubbling, isCancelable, view, event,
+                        detail, canvasRegionId, relatedTarget);
 }
 
 MouseEvent* MouseEvent::create(const AtomicString& eventType,
@@ -145,12 +112,11 @@ MouseEvent* MouseEvent::create(const AtomicString& eventType,
     modifiers = keyStateEvent->modifiers();
   }
 
-  PlatformMouseEvent::SyntheticEventType syntheticType =
-      PlatformMouseEvent::Positionless;
+  SyntheticEventType syntheticType = Positionless;
   int screenX = 0;
   int screenY = 0;
   if (underlyingEvent && underlyingEvent->isMouseEvent()) {
-    syntheticType = PlatformMouseEvent::RealOrIndistinguishable;
+    syntheticType = RealOrIndistinguishable;
     MouseEvent* mouseEvent = toMouseEvent(underlyingEvent);
     screenX = mouseEvent->screenX();
     screenY = mouseEvent->screenY();
@@ -158,14 +124,14 @@ MouseEvent* MouseEvent::create(const AtomicString& eventType,
 
   TimeTicks timestamp =
       underlyingEvent ? underlyingEvent->platformTimeStamp() : TimeTicks::Now();
-  MouseEvent* createdEvent = MouseEvent::create(
+  MouseEvent* createdEvent = new MouseEvent(
       eventType, true, true, view, 0, screenX, screenY, 0, 0, 0, 0, modifiers,
-      0, 0, nullptr, timestamp, syntheticType, String(), nullptr);
+      0, 0, nullptr, timestamp, syntheticType, String());
 
   createdEvent->setTrusted(creationScope ==
                            SimulatedClickCreationScope::FromUserAgent);
   createdEvent->setUnderlyingEvent(underlyingEvent);
-  if (syntheticType == PlatformMouseEvent::RealOrIndistinguishable) {
+  if (syntheticType == RealOrIndistinguishable) {
     MouseEvent* mouseEvent = toMouseEvent(createdEvent->underlyingEvent());
     createdEvent->initCoordinates(mouseEvent->clientX(), mouseEvent->clientY());
   }
@@ -179,62 +145,60 @@ MouseEvent::MouseEvent()
       m_button(0),
       m_buttons(0),
       m_relatedTarget(nullptr),
-      m_syntheticEventType(PlatformMouseEvent::RealOrIndistinguishable) {}
+      m_syntheticEventType(RealOrIndistinguishable) {}
 
-MouseEvent::MouseEvent(
-    const AtomicString& eventType,
-    bool canBubble,
-    bool cancelable,
-    AbstractView* abstractView,
-    PlatformMouseEvent::SyntheticEventType syntheticEventType,
-    const String& region,
-    const WebMouseEvent& event)
+MouseEvent::MouseEvent(const AtomicString& eventType,
+                       bool canBubble,
+                       bool cancelable,
+                       AbstractView* abstractView,
+                       const WebMouseEvent& event,
+                       int detail,
+                       const String& region,
+                       EventTarget* relatedTarget)
     : UIEventWithKeyState(
           eventType,
           canBubble,
           cancelable,
           abstractView,
-          0,
+          detail,
           static_cast<PlatformEvent::Modifiers>(event.modifiers()),
           TimeTicks::FromSeconds(event.timeStampSeconds()),
-          syntheticEventType == PlatformMouseEvent::FromTouch
+          event.fromTouch()
               ? InputDeviceCapabilities::firesTouchEventsSourceCapabilities()
               : InputDeviceCapabilities::
                     doesntFireTouchEventsSourceCapabilities()),
       m_screenLocation(event.globalX, event.globalY),
       m_movementDelta(flooredIntPoint(event.movementInRootFrame())),
-      m_positionType(syntheticEventType == PlatformMouseEvent::Positionless
-                         ? PositionType::Positionless
-                         : PositionType::Position),
-      m_button(0),
+      m_positionType(PositionType::Position),
+      m_button(static_cast<short>(event.button)),
       m_buttons(platformModifiersToButtons(event.modifiers())),
-      m_syntheticEventType(syntheticEventType),
+      m_relatedTarget(relatedTarget),
+      m_syntheticEventType(event.fromTouch() ? FromTouch
+                                             : RealOrIndistinguishable),
       m_region(region) {
   IntPoint rootFrameCoordinates = flooredIntPoint(event.positionInRootFrame());
   initCoordinatesFromRootFrame(rootFrameCoordinates.x(),
                                rootFrameCoordinates.y());
 }
 
-MouseEvent::MouseEvent(
-    const AtomicString& eventType,
-    bool canBubble,
-    bool cancelable,
-    AbstractView* abstractView,
-    int detail,
-    int screenX,
-    int screenY,
-    int windowX,
-    int windowY,
-    int movementX,
-    int movementY,
-    PlatformEvent::Modifiers modifiers,
-    short button,
-    unsigned short buttons,
-    EventTarget* relatedTarget,
-    TimeTicks platformTimeStamp,
-    PlatformMouseEvent::SyntheticEventType syntheticEventType,
-    const String& region,
-    const PlatformMouseEvent* mouseEvent)
+MouseEvent::MouseEvent(const AtomicString& eventType,
+                       bool canBubble,
+                       bool cancelable,
+                       AbstractView* abstractView,
+                       int detail,
+                       int screenX,
+                       int screenY,
+                       int windowX,
+                       int windowY,
+                       int movementX,
+                       int movementY,
+                       PlatformEvent::Modifiers modifiers,
+                       short button,
+                       unsigned short buttons,
+                       EventTarget* relatedTarget,
+                       TimeTicks platformTimeStamp,
+                       SyntheticEventType syntheticEventType,
+                       const String& region)
     : UIEventWithKeyState(
           eventType,
           canBubble,
@@ -243,13 +207,13 @@ MouseEvent::MouseEvent(
           detail,
           modifiers,
           platformTimeStamp,
-          syntheticEventType == PlatformMouseEvent::FromTouch
+          syntheticEventType == FromTouch
               ? InputDeviceCapabilities::firesTouchEventsSourceCapabilities()
               : InputDeviceCapabilities::
                     doesntFireTouchEventsSourceCapabilities()),
       m_screenLocation(screenX, screenY),
       m_movementDelta(movementX, movementY),
-      m_positionType(syntheticEventType == PlatformMouseEvent::Positionless
+      m_positionType(syntheticEventType == Positionless
                          ? PositionType::Positionless
                          : PositionType::Position),
       m_button(button),
@@ -257,8 +221,6 @@ MouseEvent::MouseEvent(
       m_relatedTarget(relatedTarget),
       m_syntheticEventType(syntheticEventType),
       m_region(region) {
-  if (mouseEvent)
-    m_mouseEvent.reset(new PlatformMouseEvent(*mouseEvent));
   initCoordinatesFromRootFrame(windowX, windowY);
 }
 
@@ -273,7 +235,7 @@ MouseEvent::MouseEvent(const AtomicString& eventType,
       m_button(initializer.button()),
       m_buttons(initializer.buttons()),
       m_relatedTarget(initializer.relatedTarget()),
-      m_syntheticEventType(PlatformMouseEvent::RealOrIndistinguishable),
+      m_syntheticEventType(RealOrIndistinguishable),
       m_region(initializer.region()) {
   initCoordinates(initializer.clientX(), initializer.clientY());
 }
diff --git a/third_party/WebKit/Source/core/events/MouseEvent.h b/third_party/WebKit/Source/core/events/MouseEvent.h
index 767a3409f788b7..831be6c723f3fa 100644
--- a/third_party/WebKit/Source/core/events/MouseEvent.h
+++ b/third_party/WebKit/Source/core/events/MouseEvent.h
@@ -28,7 +28,6 @@
 #include "core/events/EventDispatchMediator.h"
 #include "core/events/MouseEventInit.h"
 #include "core/events/UIEventWithKeyState.h"
-#include "platform/PlatformMouseEvent.h"
 #include "public/platform/WebMouseEvent.h"
 
 namespace blink {
@@ -39,34 +38,24 @@ class CORE_EXPORT MouseEvent : public UIEventWithKeyState {
   DEFINE_WRAPPERTYPEINFO();
 
  public:
-  static MouseEvent* create() { return new MouseEvent; }
+  enum SyntheticEventType {
+    // Real mouse input events or synthetic events that behave just like real
+    // events
+    RealOrIndistinguishable,
+    // Synthetic mouse events derived from touch input
+    FromTouch,
+    // Synthetic mouse events generated without a position, for example those
+    // generated from keyboard input.
+    Positionless,
+  };
 
-  // TODO(mustaq): Should replace most/all of these params with a
-  // MouseEventInit.
-  static MouseEvent* create(const AtomicString& type,
-                            bool canBubble,
-                            bool cancelable,
-                            AbstractView*,
-                            int detail,
-                            int screenX,
-                            int screenY,
-                            int windowX,
-                            int windowY,
-                            int movementX,
-                            int movementY,
-                            PlatformEvent::Modifiers,
-                            short button,
-                            unsigned short buttons,
-                            EventTarget* relatedTarget,
-                            TimeTicks platformTimeStamp,
-                            PlatformMouseEvent::SyntheticEventType,
-                            const String& region,
-                            const PlatformMouseEvent*);
+  static MouseEvent* create() { return new MouseEvent; }
 
   static MouseEvent* create(const AtomicString& eventType,
                             AbstractView*,
-                            const PlatformMouseEvent&,
+                            const WebMouseEvent&,
                             int detail,
+                            const String& canvasRegionId,
                             Node* relatedTarget);
 
   static MouseEvent* create(ScriptState*,
@@ -109,20 +98,17 @@ class CORE_EXPORT MouseEvent : public UIEventWithKeyState {
   void setRelatedTarget(EventTarget* relatedTarget) {
     m_relatedTarget = relatedTarget;
   }
-  PlatformMouseEvent::SyntheticEventType getSyntheticEventType() const {
+  SyntheticEventType getSyntheticEventType() const {
     return m_syntheticEventType;
   }
   const String& region() const { return m_region; }
-  void setRegion(const String& region) { m_region = region; }
 
   Node* toElement() const;
   Node* fromElement() const;
 
   virtual DataTransfer* getDataTransfer() const { return nullptr; }
 
-  bool fromTouch() const {
-    return m_syntheticEventType == PlatformMouseEvent::FromTouch;
-  }
+  bool fromTouch() const { return m_syntheticEventType == FromTouch; }
 
   const AtomicString& interfaceName() const override;
 
@@ -133,7 +119,7 @@ class CORE_EXPORT MouseEvent : public UIEventWithKeyState {
 
   int clickCount() { return detail(); }
 
-  const PlatformMouseEvent* mouseEvent() const { return m_mouseEvent.get(); }
+  const WebMouseEvent* nativeEvent() const { return m_nativeEvent.get(); }
 
   enum class PositionType {
     Position,
@@ -200,9 +186,10 @@ class CORE_EXPORT MouseEvent : public UIEventWithKeyState {
              bool canBubble,
              bool cancelable,
              AbstractView*,
-             PlatformMouseEvent::SyntheticEventType,
+             const WebMouseEvent&,
+             int detail,
              const String& region,
-             const WebMouseEvent&);
+             EventTarget* relatedTarget);
 
   MouseEvent(const AtomicString& type,
              bool canBubble,
@@ -220,9 +207,8 @@ class CORE_EXPORT MouseEvent : public UIEventWithKeyState {
              unsigned short buttons,
              EventTarget* relatedTarget,
              TimeTicks platformTimeStamp,
-             PlatformMouseEvent::SyntheticEventType,
-             const String& region,
-             const PlatformMouseEvent*);
+             SyntheticEventType,
+             const String& region);
 
   MouseEvent(const AtomicString& type, const MouseEventInit&);
 
@@ -267,9 +253,9 @@ class CORE_EXPORT MouseEvent : public UIEventWithKeyState {
   short m_button;
   unsigned short m_buttons;
   Member<EventTarget> m_relatedTarget;
-  PlatformMouseEvent::SyntheticEventType m_syntheticEventType;
+  SyntheticEventType m_syntheticEventType;
   String m_region;
-  std::unique_ptr<PlatformMouseEvent> m_mouseEvent;
+  std::unique_ptr<WebMouseEvent> m_nativeEvent;
 };
 
 class MouseEventDispatchMediator final : public EventDispatchMediator {
diff --git a/third_party/WebKit/Source/core/events/PointerEventFactory.cpp b/third_party/WebKit/Source/core/events/PointerEventFactory.cpp
index 13eed8ba6437e2..75586e7bb0eb91 100644
--- a/third_party/WebKit/Source/core/events/PointerEventFactory.cpp
+++ b/third_party/WebKit/Source/core/events/PointerEventFactory.cpp
@@ -134,22 +134,22 @@ void updateTouchPointerEventInit(const WebTouchPoint& touchPoint,
   pointerEventInit->setTwist(touchPoint.twist);
 }
 
-void updateMousePointerEventInit(const PlatformMouseEvent& mouseEvent,
+void updateMousePointerEventInit(const WebMouseEvent& mouseEvent,
                                  LocalDOMWindow* view,
                                  PointerEventInit* pointerEventInit) {
   // This function should not update attributes like pointerId, isPrimary,
   // and pointerType which is the same among the coalesced events and the
   // dispatched event.
 
-  pointerEventInit->setScreenX(mouseEvent.globalPosition().x());
-  pointerEventInit->setScreenY(mouseEvent.globalPosition().y());
+  pointerEventInit->setScreenX(mouseEvent.globalX);
+  pointerEventInit->setScreenY(mouseEvent.globalY);
 
   IntPoint locationInFrameZoomed;
   if (view && view->frame() && view->frame()->view()) {
     LocalFrame* frame = view->frame();
     FrameView* frameView = frame->view();
-    IntPoint locationInContents =
-        frameView->rootFrameToContents(mouseEvent.position());
+    IntPoint locationInContents = frameView->rootFrameToContents(
+        flooredIntPoint(mouseEvent.positionInRootFrame()));
     locationInFrameZoomed = frameView->contentsToFrame(locationInContents);
     float scaleFactor = 1 / frame->pageZoomFactor();
     locationInFrameZoomed.scale(scaleFactor, scaleFactor);
@@ -158,13 +158,12 @@ void updateMousePointerEventInit(const PlatformMouseEvent& mouseEvent,
   pointerEventInit->setClientX(locationInFrameZoomed.x());
   pointerEventInit->setClientY(locationInFrameZoomed.y());
 
-  pointerEventInit->setPressure(getPointerEventPressure(
-      mouseEvent.pointerProperties().force, pointerEventInit->buttons()));
-  pointerEventInit->setTiltX(mouseEvent.pointerProperties().tiltX);
-  pointerEventInit->setTiltY(mouseEvent.pointerProperties().tiltY);
-  pointerEventInit->setTangentialPressure(
-      mouseEvent.pointerProperties().tangentialPressure);
-  pointerEventInit->setTwist(mouseEvent.pointerProperties().twist);
+  pointerEventInit->setPressure(
+      getPointerEventPressure(mouseEvent.force, pointerEventInit->buttons()));
+  pointerEventInit->setTiltX(mouseEvent.tiltX);
+  pointerEventInit->setTiltY(mouseEvent.tiltY);
+  pointerEventInit->setTangentialPressure(mouseEvent.tangentialPressure);
+  pointerEventInit->setTwist(mouseEvent.twist);
 }
 
 }  // namespace
@@ -216,8 +215,8 @@ void PointerEventFactory::setEventSpecificFields(
 
 PointerEvent* PointerEventFactory::create(
     const AtomicString& mouseEventName,
-    const PlatformMouseEvent& mouseEvent,
-    const Vector<PlatformMouseEvent>& coalescedMouseEvents,
+    const WebMouseEvent& mouseEvent,
+    const Vector<WebMouseEvent>& coalescedMouseEvents,
     LocalDOMWindow* view) {
   DCHECK(mouseEventName == EventTypeNames::mousemove ||
          mouseEventName == EventTypeNames::mousedown ||
@@ -226,19 +225,18 @@ PointerEvent* PointerEventFactory::create(
   AtomicString pointerEventName =
       pointerEventNameForMouseEventName(mouseEventName);
 
-  unsigned buttons =
-      MouseEvent::platformModifiersToButtons(mouseEvent.getModifiers());
+  unsigned buttons = MouseEvent::platformModifiersToButtons(
+      static_cast<PlatformEvent::Modifiers>(mouseEvent.modifiers()));
   PointerEventInit pointerEventInit;
 
-  setIdTypeButtons(pointerEventInit, mouseEvent.pointerProperties(), buttons);
+  setIdTypeButtons(pointerEventInit, mouseEvent, buttons);
   setEventSpecificFields(pointerEventInit, pointerEventName);
 
   if (pointerEventName == EventTypeNames::pointerdown ||
       pointerEventName == EventTypeNames::pointerup) {
-    WebPointerProperties::Button button = mouseEvent.pointerProperties().button;
+    WebPointerProperties::Button button = mouseEvent.button;
     // TODO(mustaq): Fix when the spec starts supporting hovering erasers.
-    if (mouseEvent.pointerProperties().pointerType ==
-            WebPointerProperties::PointerType::Eraser &&
+    if (mouseEvent.pointerType == WebPointerProperties::PointerType::Eraser &&
         button == WebPointerProperties::Button::Left)
       button = WebPointerProperties::Button::Eraser;
     pointerEventInit.setButton(static_cast<int>(button));
@@ -248,14 +246,13 @@ PointerEvent* PointerEventFactory::create(
         static_cast<int>(WebPointerProperties::Button::NoButton));
   }
 
-  UIEventWithKeyState::setFromPlatformModifiers(pointerEventInit,
-                                                mouseEvent.getModifiers());
+  UIEventWithKeyState::setFromWebInputEventModifiers(
+      pointerEventInit,
+      static_cast<WebInputEvent::Modifiers>(mouseEvent.modifiers()));
 
   // Make sure chorded buttons fire pointermove instead of pointerup/down.
   if ((pointerEventName == EventTypeNames::pointerdown &&
-       (buttons &
-        ~buttonToButtonsBitfield(mouseEvent.pointerProperties().button)) !=
-           0) ||
+       (buttons & ~buttonToButtonsBitfield(mouseEvent.button)) != 0) ||
       (pointerEventName == EventTypeNames::pointerup && buttons != 0))
     pointerEventName = EventTypeNames::pointermove;
 
@@ -267,12 +264,10 @@ PointerEvent* PointerEventFactory::create(
   if (pointerEventName == EventTypeNames::pointermove) {
     HeapVector<Member<PointerEvent>> coalescedPointerEvents;
     for (const auto& coalescedMouseEvent : coalescedMouseEvents) {
-      DCHECK_EQ(mouseEvent.pointerProperties().id,
-                coalescedMouseEvent.pointerProperties().id);
+      DCHECK_EQ(mouseEvent.id, coalescedMouseEvent.id);
       // TODO(crbug.com/684292): We need further investigation of why the
       // following DCHECK fails.
-      // DCHECK_EQ(mouseEvent.pointerProperties().pointerType,
-      //          coalescedMouseEvent.pointerProperties().pointerType);
+      // DCHECK_EQ(mouseEvent.pointerType, coalescedMouseEvent.pointerType);
       PointerEventInit coalescedEventInit = pointerEventInit;
       updateMousePointerEventInit(coalescedMouseEvent, view,
                                   &coalescedEventInit);
diff --git a/third_party/WebKit/Source/core/events/PointerEventFactory.h b/third_party/WebKit/Source/core/events/PointerEventFactory.h
index 2f1275ec4ac597..7c9d0d726bf4c3 100644
--- a/third_party/WebKit/Source/core/events/PointerEventFactory.h
+++ b/third_party/WebKit/Source/core/events/PointerEventFactory.h
@@ -30,8 +30,8 @@ class CORE_EXPORT PointerEventFactory {
   ~PointerEventFactory();
 
   PointerEvent* create(const AtomicString& mouseEventName,
-                       const PlatformMouseEvent&,
-                       const Vector<PlatformMouseEvent>&,
+                       const WebMouseEvent&,
+                       const Vector<WebMouseEvent>&,
                        LocalDOMWindow*);
 
   PointerEvent* create(const WebTouchPoint&,
diff --git a/third_party/WebKit/Source/core/events/PointerEventFactoryTest.cpp b/third_party/WebKit/Source/core/events/PointerEventFactoryTest.cpp
index 9050098f02ea05..9ff83624f6c311 100644
--- a/third_party/WebKit/Source/core/events/PointerEventFactoryTest.cpp
+++ b/third_party/WebKit/Source/core/events/PointerEventFactoryTest.cpp
@@ -66,11 +66,11 @@ class PointerEventFactoryTest : public ::testing::Test {
                          WebTouchPoint::State);
   };
 
-  class PlatformMouseEventBuilder : public PlatformMouseEvent {
+  class WebMouseEventBuilder : public WebMouseEvent {
    public:
-    PlatformMouseEventBuilder(WebPointerProperties::PointerType,
-                              int,
-                              PlatformEvent::Modifiers);
+    WebMouseEventBuilder(WebPointerProperties::PointerType,
+                         int,
+                         PlatformEvent::Modifiers);
   };
 };
 
@@ -89,13 +89,13 @@ PointerEventFactoryTest::WebTouchPointBuilder::WebTouchPointBuilder(
   state = stateParam;
 }
 
-PointerEventFactoryTest::PlatformMouseEventBuilder::PlatformMouseEventBuilder(
-    WebPointerProperties::PointerType pointerType,
-    int id,
-    PlatformEvent::Modifiers modifiers) {
-  m_pointerProperties.pointerType = pointerType;
-  m_pointerProperties.id = id;
-  m_modifiers = modifiers;
+PointerEventFactoryTest::WebMouseEventBuilder::WebMouseEventBuilder(
+    WebPointerProperties::PointerType pointerTypeParam,
+    int idParam,
+    PlatformEvent::Modifiers modifiersParam) {
+  pointerType = pointerTypeParam;
+  id = idParam;
+  m_modifiers = modifiersParam;
 }
 
 PointerEvent* PointerEventFactoryTest::createAndCheckTouchCancel(
@@ -160,17 +160,16 @@ PointerEvent* PointerEventFactoryTest::createAndCheckMouseEvent(
     bool isPrimary,
     PlatformEvent::Modifiers modifiers,
     size_t coalescedEventCount) {
-  Vector<PlatformMouseEvent> coalescedEvents;
+  Vector<WebMouseEvent> coalescedEvents;
   for (size_t i = 0; i < coalescedEventCount; i++) {
-    coalescedEvents.push_back(
-        PointerEventFactoryTest::PlatformMouseEventBuilder(pointerType, rawId,
-                                                           modifiers));
+    coalescedEvents.push_back(PointerEventFactoryTest::WebMouseEventBuilder(
+        pointerType, rawId, modifiers));
   }
   PointerEvent* pointerEvent = m_pointerEventFactory.create(
       coalescedEventCount ? EventTypeNames::mousemove
                           : EventTypeNames::mousedown,
-      PointerEventFactoryTest::PlatformMouseEventBuilder(pointerType, rawId,
-                                                         modifiers),
+      PointerEventFactoryTest::WebMouseEventBuilder(pointerType, rawId,
+                                                    modifiers),
       coalescedEvents, nullptr);
   EXPECT_EQ(uniqueId, pointerEvent->pointerId());
   EXPECT_EQ(isPrimary, pointerEvent->isPrimary());
diff --git a/third_party/WebKit/Source/core/events/WheelEvent.cpp b/third_party/WebKit/Source/core/events/WheelEvent.cpp
index 5f39f8bfb960bd..3597836380a3f2 100644
--- a/third_party/WebKit/Source/core/events/WheelEvent.cpp
+++ b/third_party/WebKit/Source/core/events/WheelEvent.cpp
@@ -24,7 +24,6 @@
 #include "core/events/WheelEvent.h"
 
 #include "core/clipboard/DataTransfer.h"
-#include "platform/PlatformMouseEvent.h"
 
 namespace blink {
 
@@ -73,12 +72,13 @@ WheelEvent::WheelEvent(const WebMouseWheelEvent& event, AbstractView* view)
                  true,
                  event.isCancelable(),
                  view,
-                 PlatformMouseEvent::RealOrIndistinguishable,
+                 event,
+                 event.clickCount,
                  // TODO(zino): Should support canvas hit region because the
                  // wheel event is a kind of mouse event. Please see
                  // http://crbug.com/594075
                  String(),
-                 event),
+                 nullptr),
       m_wheelDelta(event.wheelTicksX * TickMultiplier,
                    event.wheelTicksY * TickMultiplier),
       m_deltaX(-event.deltaXInRootFrame()),
diff --git a/third_party/WebKit/Source/core/html/HTMLInputElement.cpp b/third_party/WebKit/Source/core/html/HTMLInputElement.cpp
index 07ee1a2913f461..af78e1d7cecd1c 100644
--- a/third_party/WebKit/Source/core/html/HTMLInputElement.cpp
+++ b/third_party/WebKit/Source/core/html/HTMLInputElement.cpp
@@ -72,7 +72,6 @@
 #include "core/layout/LayoutTheme.h"
 #include "core/page/ChromeClient.h"
 #include "platform/Language.h"
-#include "platform/PlatformMouseEvent.h"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/text/PlatformLocale.h"
 #include "wtf/MathExtras.h"
diff --git a/third_party/WebKit/Source/core/html/HTMLSelectElement.cpp b/third_party/WebKit/Source/core/html/HTMLSelectElement.cpp
index db8af6744e0bbc..6489494298abf1 100644
--- a/third_party/WebKit/Source/core/html/HTMLSelectElement.cpp
+++ b/third_party/WebKit/Source/core/html/HTMLSelectElement.cpp
@@ -70,7 +70,6 @@
 #include "core/page/ChromeClient.h"
 #include "core/page/Page.h"
 #include "core/page/SpatialNavigation.h"
-#include "platform/PlatformMouseEvent.h"
 #include "platform/PopupMenu.h"
 #include "platform/instrumentation/tracing/TraceEvent.h"
 #include "platform/text/PlatformLocale.h"
@@ -1288,7 +1287,7 @@ void HTMLSelectElement::menuListDefaultEventHandler(Event* event) {
       return;
 
     int ignoreModifiers = PlatformEvent::ShiftKey | PlatformEvent::CtrlKey |
-                          PlatformEvent::AltKey | PlatformMouseEvent::MetaKey;
+                          PlatformEvent::AltKey | PlatformEvent::MetaKey;
     if (keyEvent->modifiers() & ignoreModifiers)
       return;
 
diff --git a/third_party/WebKit/Source/core/html/forms/RangeInputType.cpp b/third_party/WebKit/Source/core/html/forms/RangeInputType.cpp
index 0ca1bd5e0073fb..e2a50b29a0844a 100644
--- a/third_party/WebKit/Source/core/html/forms/RangeInputType.cpp
+++ b/third_party/WebKit/Source/core/html/forms/RangeInputType.cpp
@@ -50,7 +50,6 @@
 #include "core/html/shadow/ShadowElementNames.h"
 #include "core/html/shadow/SliderThumbElement.h"
 #include "core/layout/LayoutSlider.h"
-#include "platform/PlatformMouseEvent.h"
 #include "wtf/MathExtras.h"
 #include "wtf/NonCopyingSort.h"
 #include <limits>
diff --git a/third_party/WebKit/Source/core/input/EventHandler.cpp b/third_party/WebKit/Source/core/input/EventHandler.cpp
index 35cea31c489be6..1d310088b319f7 100644
--- a/third_party/WebKit/Source/core/input/EventHandler.cpp
+++ b/third_party/WebKit/Source/core/input/EventHandler.cpp
@@ -568,14 +568,13 @@ OptionalCursor EventHandler::selectAutoCursor(const HitTestResult& result,
 }
 
 WebInputEventResult EventHandler::handleMousePressEvent(
-    const PlatformMouseEvent& mouseEvent) {
+    const WebMouseEvent& mouseEvent) {
   TRACE_EVENT0("blink", "EventHandler::handleMousePressEvent");
 
   // For 4th/5th button in the mouse since Chrome does not yet send
   // button value to Blink but in some cases it does send the event.
   // This check is needed to suppress such an event (crbug.com/574959)
-  if (mouseEvent.pointerProperties().button ==
-      WebPointerProperties::Button::NoButton)
+  if (mouseEvent.button == WebPointerProperties::Button::NoButton)
     return WebInputEventResult::HandledSuppressed;
 
   if (m_eventHandlerWillResetCapturingMouseEventsNode)
@@ -588,8 +587,8 @@ WebInputEventResult EventHandler::handleMousePressEvent(
   HitTestRequest request(HitTestRequest::Active);
   // Save the document point we generate in case the window coordinate is
   // invalidated by what happens when we dispatch the event.
-  LayoutPoint documentPoint =
-      m_frame->view()->rootFrameToContents(mouseEvent.position());
+  LayoutPoint documentPoint = m_frame->view()->rootFrameToContents(
+      flooredIntPoint(mouseEvent.positionInRootFrame()));
   MouseEventWithHitTestResults mev =
       m_frame->document()->performMouseEventHitTest(request, documentPoint,
                                                     mouseEvent);
@@ -642,7 +641,7 @@ WebInputEventResult EventHandler::handleMousePressEvent(
     }
   }
 
-  m_mouseEventManager->setClickCount(mouseEvent.clickCount());
+  m_mouseEventManager->setClickCount(mouseEvent.clickCount);
   m_mouseEventManager->setClickNode(
       mev.innerNode()->isTextNode()
           ? FlatTreeTraversal::parent(*mev.innerNode())
@@ -652,15 +651,16 @@ WebInputEventResult EventHandler::handleMousePressEvent(
     m_frame->selection().setCaretBlinkingSuspended(true);
 
   WebInputEventResult eventResult = updatePointerTargetAndDispatchEvents(
-      EventTypeNames::mousedown, mev.innerNode(), mev.event(),
-      Vector<PlatformMouseEvent>());
+      EventTypeNames::mousedown, mev.innerNode(), mev.canvasRegionId(),
+      mev.event(), Vector<WebMouseEvent>());
 
   if (eventResult == WebInputEventResult::NotHandled && m_frame->view()) {
     FrameView* view = m_frame->view();
     PaintLayer* layer = mev.innerNode()->layoutObject()
                             ? mev.innerNode()->layoutObject()->enclosingLayer()
                             : nullptr;
-    IntPoint p = view->rootFrameToContents(mouseEvent.position());
+    IntPoint p = view->rootFrameToContents(
+        flooredIntPoint(mouseEvent.positionInRootFrame()));
     if (layer && layer->getScrollableArea() &&
         layer->getScrollableArea()->isPointInResizeControl(p,
                                                            ResizerForPointer)) {
@@ -678,7 +678,7 @@ WebInputEventResult EventHandler::handleMousePressEvent(
   HitTestResult hitTestResult = EventHandlingUtil::hitTestResultInFrame(
       m_frame, documentPoint, HitTestRequest::ReadOnly);
   InputDeviceCapabilities* sourceCapabilities =
-      mouseEvent.getSyntheticEventType() == PlatformMouseEvent::FromTouch
+      mouseEvent.fromTouch()
           ? InputDeviceCapabilities::firesTouchEventsSourceCapabilities()
           : InputDeviceCapabilities::doesntFireTouchEventsSourceCapabilities();
   if (eventResult == WebInputEventResult::NotHandled) {
@@ -719,9 +719,8 @@ WebInputEventResult EventHandler::handleMousePressEvent(
   }
 
   if (mev.hitTestResult().innerNode() &&
-      mouseEvent.pointerProperties().button ==
-          WebPointerProperties::Button::Left) {
-    ASSERT(mouseEvent.type() == PlatformEvent::MousePressed);
+      mouseEvent.button == WebPointerProperties::Button::Left) {
+    DCHECK_EQ(WebInputEvent::MouseDown, mouseEvent.type());
     HitTestResult result = mev.hitTestResult();
     result.setToShadowHostIfInUserAgentShadowRoot();
     m_frame->chromeClient().onMouseDown(result.innerNode());
@@ -731,8 +730,8 @@ WebInputEventResult EventHandler::handleMousePressEvent(
 }
 
 WebInputEventResult EventHandler::handleMouseMoveEvent(
-    const PlatformMouseEvent& event,
-    const Vector<PlatformMouseEvent>& coalescedEvents) {
+    const WebMouseEvent& event,
+    const Vector<WebMouseEvent>& coalescedEvents) {
   TRACE_EVENT0("blink", "EventHandler::handleMouseMoveEvent");
 
   HitTestResult hoveredNode = HitTestResult();
@@ -759,16 +758,15 @@ WebInputEventResult EventHandler::handleMouseMoveEvent(
   return result;
 }
 
-void EventHandler::handleMouseLeaveEvent(const PlatformMouseEvent& event) {
+void EventHandler::handleMouseLeaveEvent(const WebMouseEvent& event) {
   TRACE_EVENT0("blink", "EventHandler::handleMouseLeaveEvent");
 
-  handleMouseMoveOrLeaveEvent(event, Vector<PlatformMouseEvent>(), 0, false,
-                              true);
+  handleMouseMoveOrLeaveEvent(event, Vector<WebMouseEvent>(), 0, false, true);
 }
 
 WebInputEventResult EventHandler::handleMouseMoveOrLeaveEvent(
-    const PlatformMouseEvent& mouseEvent,
-    const Vector<PlatformMouseEvent>& coalescedEvents,
+    const WebMouseEvent& mouseEvent,
+    const Vector<WebMouseEvent>& coalescedEvents,
     HitTestResult* hoveredNode,
     bool onlyUpdateScrollbars,
     bool forceLeave) {
@@ -784,9 +782,9 @@ WebInputEventResult EventHandler::handleMouseMoveOrLeaveEvent(
   m_mouseEventManager->handleSvgPanIfNeeded(false);
 
   if (m_frameSetBeingResized) {
-    return updatePointerTargetAndDispatchEvents(EventTypeNames::mousemove,
-                                                m_frameSetBeingResized.get(),
-                                                mouseEvent, coalescedEvents);
+    return updatePointerTargetAndDispatchEvents(
+        EventTypeNames::mousemove, m_frameSetBeingResized.get(), String(),
+        mouseEvent, coalescedEvents);
   }
 
   // Send events right to a scrollbar if the mouse is pressed.
@@ -862,7 +860,8 @@ WebInputEventResult EventHandler::handleMouseMoveOrLeaveEvent(
   if (newSubframe) {
     // Update over/out state before passing the event to the subframe.
     m_pointerEventManager->sendMouseAndPointerBoundaryEvents(
-        updateMouseEventTargetNode(mev.innerNode()), mev.event());
+        updateMouseEventTargetNode(mev.innerNode()), mev.canvasRegionId(),
+        mev.event());
 
     // Event dispatch in sendMouseAndPointerBoundaryEvents may have caused the
     // subframe of the target node to be detached from its FrameView, in which
@@ -891,7 +890,8 @@ WebInputEventResult EventHandler::handleMouseMoveOrLeaveEvent(
     return eventResult;
 
   eventResult = updatePointerTargetAndDispatchEvents(
-      EventTypeNames::mousemove, mev.innerNode(), mev.event(), coalescedEvents);
+      EventTypeNames::mousemove, mev.innerNode(), mev.canvasRegionId(),
+      mev.event(), coalescedEvents);
   if (eventResult != WebInputEventResult::NotHandled)
     return eventResult;
 
@@ -899,14 +899,13 @@ WebInputEventResult EventHandler::handleMouseMoveOrLeaveEvent(
 }
 
 WebInputEventResult EventHandler::handleMouseReleaseEvent(
-    const PlatformMouseEvent& mouseEvent) {
+    const WebMouseEvent& mouseEvent) {
   TRACE_EVENT0("blink", "EventHandler::handleMouseReleaseEvent");
 
   // For 4th/5th button in the mouse since Chrome does not yet send
   // button value to Blink but in some cases it does send the event.
   // This check is needed to suppress such an event (crbug.com/574959)
-  if (mouseEvent.pointerProperties().button ==
-      WebPointerProperties::Button::NoButton)
+  if (mouseEvent.button == WebPointerProperties::Button::NoButton)
     return WebInputEventResult::HandledSuppressed;
 
   if (!mouseEvent.fromTouch())
@@ -924,7 +923,7 @@ WebInputEventResult EventHandler::handleMouseReleaseEvent(
 
   if (m_frameSetBeingResized) {
     return m_mouseEventManager->setMousePositionAndDispatchMouseEvent(
-        updateMouseEventTargetNode(m_frameSetBeingResized.get()),
+        updateMouseEventTargetNode(m_frameSetBeingResized.get()), String(),
         EventTypeNames::mouseup, mouseEvent);
   }
 
@@ -933,7 +932,7 @@ WebInputEventResult EventHandler::handleMouseReleaseEvent(
     m_lastScrollbarUnderMouse->mouseUp(mouseEvent);
     return updatePointerTargetAndDispatchEvents(
         EventTypeNames::mouseup, m_mouseEventManager->getNodeUnderMouse(),
-        mouseEvent, Vector<PlatformMouseEvent>());
+        String(), mouseEvent, Vector<WebMouseEvent>());
   }
 
   // Mouse events simulated from touch should not hit-test again.
@@ -971,8 +970,8 @@ WebInputEventResult EventHandler::handleMouseReleaseEvent(
   }
 
   WebInputEventResult eventResult = updatePointerTargetAndDispatchEvents(
-      EventTypeNames::mouseup, mev.innerNode(), mev.event(),
-      Vector<PlatformMouseEvent>());
+      EventTypeNames::mouseup, mev.innerNode(), mev.canvasRegionId(),
+      mev.event(), Vector<WebMouseEvent>());
 
   WebInputEventResult clickEventResult =
       m_mouseEventManager->dispatchMouseClickIfNeeded(mev);
@@ -1044,7 +1043,7 @@ static bool findDropZone(Node* target, DataTransfer* dataTransfer) {
 }
 
 WebInputEventResult EventHandler::updateDragAndDrop(
-    const PlatformMouseEvent& event,
+    const WebMouseEvent& event,
     DataTransfer* dataTransfer) {
   WebInputEventResult eventResult = WebInputEventResult::NotHandled;
 
@@ -1062,9 +1061,11 @@ WebInputEventResult EventHandler::updateDragAndDrop(
     newTarget = FlatTreeTraversal::parent(*newTarget);
 
   if (AutoscrollController* controller =
-          m_scrollManager->autoscrollController())
-    controller->updateDragAndDrop(newTarget, event.position(),
-                                  event.timestamp());
+          m_scrollManager->autoscrollController()) {
+    controller->updateDragAndDrop(
+        newTarget, flooredIntPoint(event.positionInRootFrame()),
+        TimeTicks::FromSeconds(event.timeStampSeconds()));
+  }
 
   if (m_dragTarget != newTarget) {
     // FIXME: this ordering was explicitly chosen to match WinIE. However,
@@ -1137,7 +1138,7 @@ WebInputEventResult EventHandler::updateDragAndDrop(
   return eventResult;
 }
 
-void EventHandler::cancelDragAndDrop(const PlatformMouseEvent& event,
+void EventHandler::cancelDragAndDrop(const WebMouseEvent& event,
                                      DataTransfer* dataTransfer) {
   LocalFrame* targetFrame;
   if (targetIsFrame(m_dragTarget.get(), targetFrame)) {
@@ -1153,7 +1154,7 @@ void EventHandler::cancelDragAndDrop(const PlatformMouseEvent& event,
 }
 
 WebInputEventResult EventHandler::performDragAndDrop(
-    const PlatformMouseEvent& event,
+    const WebMouseEvent& event,
     DataTransfer* dataTransfer) {
   LocalFrame* targetFrame;
   WebInputEventResult result = WebInputEventResult::NotHandled;
@@ -1256,15 +1257,16 @@ void EventHandler::elementRemoved(EventTarget* target) {
 WebInputEventResult EventHandler::updatePointerTargetAndDispatchEvents(
     const AtomicString& mouseEventType,
     Node* targetNode,
-    const PlatformMouseEvent& mouseEvent,
-    const Vector<PlatformMouseEvent>& coalescedEvents) {
+    const String& canvasRegionId,
+    const WebMouseEvent& mouseEvent,
+    const Vector<WebMouseEvent>& coalescedEvents) {
   ASSERT(mouseEventType == EventTypeNames::mousedown ||
          mouseEventType == EventTypeNames::mousemove ||
          mouseEventType == EventTypeNames::mouseup);
 
   const auto& eventResult = m_pointerEventManager->sendMousePointerEvent(
-      updateMouseEventTargetNode(targetNode), mouseEventType, mouseEvent,
-      coalescedEvents);
+      updateMouseEventTargetNode(targetNode), canvasRegionId, mouseEventType,
+      mouseEvent, coalescedEvents);
   return eventResult;
 }
 
@@ -1617,33 +1619,33 @@ void EventHandler::updateGestureTargetNodeForMouseEvent(
 
   const WebGestureEvent& gestureEvent = targetedEvent.event();
   unsigned modifiers = gestureEvent.modifiers();
-  PlatformMouseEvent fakeMouseMove(
-      gestureEvent, WebPointerProperties::Button::NoButton,
-      PlatformEvent::MouseMoved,
-      /* clickCount */ 0, static_cast<PlatformEvent::Modifiers>(modifiers),
-      PlatformMouseEvent::FromTouch,
-      TimeTicks::FromSeconds(gestureEvent.timeStampSeconds()),
-      WebPointerProperties::PointerType::Mouse);
+  WebMouseEvent fakeMouseMove(
+      WebInputEvent::MouseMove, gestureEvent,
+      WebPointerProperties::Button::NoButton,
+      /* clickCount */ 0,
+      modifiers | WebInputEvent::Modifiers::IsCompatibilityEventForTouch,
+      gestureEvent.timeStampSeconds());
 
   // Update the mouseout/mouseleave event
   size_t indexExitedFrameChain = exitedFrameChain.size();
   while (indexExitedFrameChain) {
     LocalFrame* leaveFrame = exitedFrameChain[--indexExitedFrameChain];
     leaveFrame->eventHandler().m_mouseEventManager->setNodeUnderMouse(
-        updateMouseEventTargetNode(nullptr), fakeMouseMove);
+        updateMouseEventTargetNode(nullptr), String(), fakeMouseMove);
   }
 
   // update the mouseover/mouseenter event
   while (indexEnteredFrameChain) {
     Frame* parentFrame =
         enteredFrameChain[--indexEnteredFrameChain]->tree().parent();
-    if (parentFrame && parentFrame->isLocalFrame())
+    if (parentFrame && parentFrame->isLocalFrame()) {
       toLocalFrame(parentFrame)
           ->eventHandler()
           .m_mouseEventManager->setNodeUnderMouse(
               updateMouseEventTargetNode(toHTMLFrameOwnerElement(
                   enteredFrameChain[indexEnteredFrameChain]->owner())),
-              fakeMouseMove);
+              String(), fakeMouseMove);
+    }
   }
 }
 
@@ -1782,7 +1784,7 @@ void EventHandler::applyTouchAdjustment(WebGestureEvent* gestureEvent,
 }
 
 WebInputEventResult EventHandler::sendContextMenuEvent(
-    const PlatformMouseEvent& event,
+    const WebMouseEvent& event,
     Node* overrideTargetNode) {
   FrameView* v = m_frame->view();
   if (!v)
@@ -1791,7 +1793,8 @@ WebInputEventResult EventHandler::sendContextMenuEvent(
   // Clear mouse press state to avoid initiating a drag while context menu is
   // up.
   m_mouseEventManager->setMousePressed(false);
-  LayoutPoint positionInContents = v->rootFrameToContents(event.position());
+  LayoutPoint positionInContents =
+      v->rootFrameToContents(flooredIntPoint(event.positionInRootFrame()));
   HitTestRequest request(HitTestRequest::Active);
   MouseEventWithHitTestResults mev =
       m_frame->document()->performMouseEventHitTest(request, positionInContents,
@@ -1806,7 +1809,7 @@ WebInputEventResult EventHandler::sendContextMenuEvent(
   Node* targetNode = overrideTargetNode ? overrideTargetNode : mev.innerNode();
   return m_mouseEventManager->dispatchMouseEvent(
       updateMouseEventTargetNode(targetNode), EventTypeNames::contextmenu,
-      event, 0);
+      event, mev.hitTestResult().canvasRegionId(), 0);
 }
 
 WebInputEventResult EventHandler::sendContextMenuEventForKey(
@@ -1883,15 +1886,20 @@ WebInputEventResult EventHandler::sendContextMenuEventForKey(
 
   // The contextmenu event is a mouse event even when invoked using the
   // keyboard.  This is required for web compatibility.
-  PlatformEvent::EventType eventType = PlatformEvent::MousePressed;
+  WebInputEvent::Type eventType = WebInputEvent::MouseDown;
   if (m_frame->settings() && m_frame->settings()->getShowContextMenuOnMouseUp())
-    eventType = PlatformEvent::MouseReleased;
+    eventType = WebInputEvent::MouseUp;
+
+  WebMouseEvent mouseEvent(
+      eventType,
+      WebFloatPoint(locationInRootFrame.x(), locationInRootFrame.y()),
+      WebFloatPoint(globalPosition.x(), globalPosition.y()),
+      WebPointerProperties::Button::NoButton, /* clickCount */ 0,
+      PlatformEvent::NoModifiers, TimeTicks::Now().InSeconds());
 
-  PlatformMouseEvent mouseEvent(
-      locationInRootFrame, globalPosition,
-      WebPointerProperties::Button::NoButton, eventType, /* clickCount */ 0,
-      PlatformEvent::NoModifiers, PlatformMouseEvent::RealOrIndistinguishable,
-      TimeTicks::Now(), WebPointerProperties::PointerType::Mouse);
+  // TODO(dtapuska): Transition the mouseEvent to be created really in viewport
+  // coordinates instead of root frame coordinates.
+  mouseEvent.setFrameScale(1);
 
   return sendContextMenuEvent(mouseEvent, overrideTargetElement);
 }
@@ -1987,7 +1995,7 @@ void EventHandler::defaultKeyboardEventHandler(KeyboardEvent* event) {
       event, m_mouseEventManager->mousePressNode());
 }
 
-void EventHandler::dragSourceEndedAt(const PlatformMouseEvent& event,
+void EventHandler::dragSourceEndedAt(const WebMouseEvent& event,
                                      DragOperation operation) {
   // Asides from routing the event to the correct frame, the hit test is also an
   // opportunity for Layer to update the :hover and :active pseudoclasses.
@@ -2100,7 +2108,7 @@ WebInputEventResult EventHandler::passMousePressEventToSubframe(
 
 WebInputEventResult EventHandler::passMouseMoveEventToSubframe(
     MouseEventWithHitTestResults& mev,
-    const Vector<PlatformMouseEvent>& coalescedEvents,
+    const Vector<WebMouseEvent>& coalescedEvents,
     LocalFrame* subframe,
     HitTestResult* hoveredNode) {
   if (m_mouseEventManager->mouseDownMayStartDrag())
diff --git a/third_party/WebKit/Source/core/input/EventHandler.h b/third_party/WebKit/Source/core/input/EventHandler.h
index 152219ddecb379..6b52de472203e7 100644
--- a/third_party/WebKit/Source/core/input/EventHandler.h
+++ b/third_party/WebKit/Source/core/input/EventHandler.h
@@ -38,7 +38,6 @@
 #include "core/page/EventWithHitTestResults.h"
 #include "core/style/ComputedStyleConstants.h"
 #include "platform/Cursor.h"
-#include "platform/PlatformMouseEvent.h"
 #include "platform/UserGestureIndicator.h"
 #include "platform/geometry/LayoutPoint.h"
 #include "platform/heap/Handle.h"
@@ -73,6 +72,7 @@ class Scrollbar;
 class SelectionController;
 class TextEvent;
 class WebGestureEvent;
+class WebMouseEvent;
 class WebMouseWheelEvent;
 class WebTouchEvent;
 
@@ -113,11 +113,9 @@ class CORE_EXPORT EventHandler final
   void setCapturingMouseEventsNode(
       Node*);  // A caller is responsible for resetting capturing node to 0.
 
-  WebInputEventResult updateDragAndDrop(const PlatformMouseEvent&,
-                                        DataTransfer*);
-  void cancelDragAndDrop(const PlatformMouseEvent&, DataTransfer*);
-  WebInputEventResult performDragAndDrop(const PlatformMouseEvent&,
-                                         DataTransfer*);
+  WebInputEventResult updateDragAndDrop(const WebMouseEvent&, DataTransfer*);
+  void cancelDragAndDrop(const WebMouseEvent&, DataTransfer*);
+  WebInputEventResult performDragAndDrop(const WebMouseEvent&, DataTransfer*);
   void updateDragStateAfterEditDragIfNeeded(Element* rootEditableElement);
 
   void scheduleHoverStateUpdate();
@@ -142,12 +140,12 @@ class CORE_EXPORT EventHandler final
                       Node* startingNode = nullptr);
 
   WebInputEventResult handleMouseMoveEvent(
-      const PlatformMouseEvent&,
-      const Vector<PlatformMouseEvent>& coalescedEvents);
-  void handleMouseLeaveEvent(const PlatformMouseEvent&);
+      const WebMouseEvent&,
+      const Vector<WebMouseEvent>& coalescedEvents);
+  void handleMouseLeaveEvent(const WebMouseEvent&);
 
-  WebInputEventResult handleMousePressEvent(const PlatformMouseEvent&);
-  WebInputEventResult handleMouseReleaseEvent(const PlatformMouseEvent&);
+  WebInputEventResult handleMousePressEvent(const WebMouseEvent&);
+  WebInputEventResult handleMouseReleaseEvent(const WebMouseEvent&);
   WebInputEventResult handleWheelEvent(const WebMouseWheelEvent&);
 
   // Called on the local root frame exactly once per gesture event.
@@ -193,7 +191,7 @@ class CORE_EXPORT EventHandler final
                                      IntRect& targetArea,
                                      Node*& targetNode);
 
-  WebInputEventResult sendContextMenuEvent(const PlatformMouseEvent&,
+  WebInputEventResult sendContextMenuEvent(const WebMouseEvent&,
                                            Node* overrideTargetNode = nullptr);
   WebInputEventResult sendContextMenuEventForKey(
       Element* overrideTargetElement = nullptr);
@@ -219,7 +217,7 @@ class CORE_EXPORT EventHandler final
                             TextEventInputType = TextEventInputKeyboard);
   void defaultTextInputEventHandler(TextEvent*);
 
-  void dragSourceEndedAt(const PlatformMouseEvent&, DragOperation);
+  void dragSourceEndedAt(const WebMouseEvent&, DragOperation);
 
   void capsLockStateMayHaveChanged();  // Only called by FrameSelection
 
@@ -260,8 +258,8 @@ class CORE_EXPORT EventHandler final
 
  private:
   WebInputEventResult handleMouseMoveOrLeaveEvent(
-      const PlatformMouseEvent&,
-      const Vector<PlatformMouseEvent>&,
+      const WebMouseEvent&,
+      const Vector<WebMouseEvent>&,
       HitTestResult* hoveredNode = nullptr,
       bool onlyUpdateScrollbars = false,
       bool forceLeave = false);
@@ -302,13 +300,14 @@ class CORE_EXPORT EventHandler final
   // preventDefaulted pointerdown (i.e., one of
   // {mousedown, mousemove, mouseup}).
   // TODO(mustaq): Can we avoid the clickCount param, instead use
-  // PlatformMouseEvent's count?
+  // WebmMouseEvent's count?
   //     Same applied to dispatchMouseEvent() above.
   WebInputEventResult updatePointerTargetAndDispatchEvents(
       const AtomicString& mouseEventType,
       Node* target,
-      const PlatformMouseEvent&,
-      const Vector<PlatformMouseEvent>& coalescedEvents);
+      const String& canvasRegionId,
+      const WebMouseEvent&,
+      const Vector<WebMouseEvent>& coalescedEvents);
 
   // Clears drag target and related states. It is called when drag is done or
   // canceled.
@@ -319,7 +318,7 @@ class CORE_EXPORT EventHandler final
       LocalFrame* subframe);
   WebInputEventResult passMouseMoveEventToSubframe(
       MouseEventWithHitTestResults&,
-      const Vector<PlatformMouseEvent>&,
+      const Vector<WebMouseEvent>&,
       LocalFrame* subframe,
       HitTestResult* hoveredNode = nullptr);
   WebInputEventResult passMouseReleaseEventToSubframe(
diff --git a/third_party/WebKit/Source/core/input/EventHandlerTest.cpp b/third_party/WebKit/Source/core/input/EventHandlerTest.cpp
index 8ff61f1149f03e..e92bcffb1bba1b 100644
--- a/third_party/WebKit/Source/core/input/EventHandlerTest.cpp
+++ b/third_party/WebKit/Source/core/input/EventHandlerTest.cpp
@@ -14,7 +14,6 @@
 #include "core/page/AutoscrollController.h"
 #include "core/page/Page.h"
 #include "core/testing/DummyPageHolder.h"
-#include "platform/PlatformMouseEvent.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include <memory>
 
@@ -63,18 +62,20 @@ class LongPressEventBuilder : public WebGestureEvent {
   }
 };
 
-class MousePressEventBuilder : public PlatformMouseEvent {
+class MousePressEventBuilder : public WebMouseEvent {
  public:
   MousePressEventBuilder(IntPoint position,
-                         int clickCount,
-                         WebMouseEvent::Button button)
-      : PlatformMouseEvent(position,
-                           position,
-                           button,
-                           PlatformEvent::MousePressed,
-                           clickCount,
-                           static_cast<PlatformEvent::Modifiers>(0),
-                           TimeTicks::Now()) {}
+                         int clickCountParam,
+                         WebMouseEvent::Button buttonParam)
+      : WebMouseEvent(WebInputEvent::MouseDown,
+                      WebInputEvent::NoModifiers,
+                      TimeTicks::Now().InSeconds()) {
+    clickCount = clickCountParam;
+    button = buttonParam;
+    x = globalX = position.x();
+    y = globalY = position.y();
+    m_frameScale = 1;
+  }
 };
 
 void EventHandlerTest::SetUp() {
@@ -105,27 +106,32 @@ TEST_F(EventHandlerTest, dragSelectionAfterScroll) {
   frameView->layoutViewportScrollableArea()->setScrollOffset(
       ScrollOffset(0, 400), ProgrammaticScroll);
 
-  PlatformMouseEvent mouseDownEvent(
-      IntPoint(0, 0), IntPoint(100, 200), WebPointerProperties::Button::Left,
-      PlatformEvent::MousePressed, 1, PlatformEvent::Modifiers::LeftButtonDown,
-      TimeTicks::Now());
+  WebMouseEvent mouseDownEvent(WebInputEvent::MouseDown, WebFloatPoint(0, 0),
+                               WebFloatPoint(100, 200),
+                               WebPointerProperties::Button::Left, 1,
+                               WebInputEvent::Modifiers::LeftButtonDown,
+                               WebInputEvent::TimeStampForTesting);
+  mouseDownEvent.setFrameScale(1);
   document().frame()->eventHandler().handleMousePressEvent(mouseDownEvent);
 
-  PlatformMouseEvent mouseMoveEvent(
-      IntPoint(100, 50), IntPoint(200, 250), WebPointerProperties::Button::Left,
-      PlatformEvent::MouseMoved, 1, PlatformEvent::Modifiers::LeftButtonDown,
-      TimeTicks::Now());
+  WebMouseEvent mouseMoveEvent(WebInputEvent::MouseMove, WebFloatPoint(100, 50),
+                               WebFloatPoint(200, 250),
+                               WebPointerProperties::Button::Left, 1,
+                               WebInputEvent::Modifiers::LeftButtonDown,
+                               WebInputEvent::TimeStampForTesting);
+  mouseMoveEvent.setFrameScale(1);
   document().frame()->eventHandler().handleMouseMoveEvent(
-      mouseMoveEvent, Vector<PlatformMouseEvent>());
+      mouseMoveEvent, Vector<WebMouseEvent>());
 
   page().autoscrollController().animate(WTF::monotonicallyIncreasingTime());
   page().animator().serviceScriptedAnimations(
       WTF::monotonicallyIncreasingTime());
 
-  PlatformMouseEvent mouseUpEvent(
-      IntPoint(100, 50), IntPoint(200, 250), WebPointerProperties::Button::Left,
-      PlatformEvent::MouseReleased, 1, static_cast<PlatformEvent::Modifiers>(0),
-      TimeTicks::Now());
+  WebMouseEvent mouseUpEvent(
+      WebMouseEvent::MouseUp, WebFloatPoint(100, 50), WebFloatPoint(200, 250),
+      WebPointerProperties::Button::Left, 1, WebInputEvent::NoModifiers,
+      WebInputEvent::TimeStampForTesting);
+  mouseUpEvent.setFrameScale(1);
   document().frame()->eventHandler().handleMouseReleaseEvent(mouseUpEvent);
 
   ASSERT_TRUE(selection().isRange());
@@ -206,18 +212,22 @@ TEST_F(EventHandlerTest, draggedInlinePositionTest) {
       "<div style='width: 300px; height: 100px;'>"
       "<span class='line' draggable='true'>abcd</span>"
       "</div>");
-  PlatformMouseEvent mouseDownEvent(
-      IntPoint(262, 29), IntPoint(329, 67), WebPointerProperties::Button::Left,
-      PlatformEvent::MousePressed, 1, PlatformEvent::Modifiers::LeftButtonDown,
-      TimeTicks::Now());
+  WebMouseEvent mouseDownEvent(WebMouseEvent::MouseDown, WebFloatPoint(262, 29),
+                               WebFloatPoint(329, 67),
+                               WebPointerProperties::Button::Left, 1,
+                               WebInputEvent::Modifiers::LeftButtonDown,
+                               WebInputEvent::TimeStampForTesting);
+  mouseDownEvent.setFrameScale(1);
   document().frame()->eventHandler().handleMousePressEvent(mouseDownEvent);
 
-  PlatformMouseEvent mouseMoveEvent(
-      IntPoint(618, 298), IntPoint(685, 436),
-      WebPointerProperties::Button::Left, PlatformEvent::MouseMoved, 1,
-      PlatformEvent::Modifiers::LeftButtonDown, TimeTicks::Now());
+  WebMouseEvent mouseMoveEvent(WebMouseEvent::MouseMove,
+                               WebFloatPoint(618, 298), WebFloatPoint(685, 436),
+                               WebPointerProperties::Button::Left, 1,
+                               WebInputEvent::Modifiers::LeftButtonDown,
+                               WebInputEvent::TimeStampForTesting);
+  mouseMoveEvent.setFrameScale(1);
   document().frame()->eventHandler().handleMouseMoveEvent(
-      mouseMoveEvent, Vector<PlatformMouseEvent>());
+      mouseMoveEvent, Vector<WebMouseEvent>());
 
   EXPECT_EQ(
       IntPoint(12, 29),
@@ -238,18 +248,22 @@ TEST_F(EventHandlerTest, draggedSVGImagePositionTest) {
       "draggable='true'/>"
       "</svg>"
       "</div>");
-  PlatformMouseEvent mouseDownEvent(
-      IntPoint(145, 144), IntPoint(212, 282),
-      WebPointerProperties::Button::Left, PlatformEvent::MousePressed, 1,
-      PlatformEvent::Modifiers::LeftButtonDown, TimeTicks::Now());
+  WebMouseEvent mouseDownEvent(WebMouseEvent::MouseDown,
+                               WebFloatPoint(145, 144), WebFloatPoint(212, 282),
+                               WebPointerProperties::Button::Left, 1,
+                               WebInputEvent::Modifiers::LeftButtonDown,
+                               WebInputEvent::TimeStampForTesting);
+  mouseDownEvent.setFrameScale(1);
   document().frame()->eventHandler().handleMousePressEvent(mouseDownEvent);
 
-  PlatformMouseEvent mouseMoveEvent(
-      IntPoint(618, 298), IntPoint(685, 436),
-      WebPointerProperties::Button::Left, PlatformEvent::MouseMoved, 1,
-      PlatformEvent::Modifiers::LeftButtonDown, TimeTicks::Now());
+  WebMouseEvent mouseMoveEvent(WebMouseEvent::MouseMove,
+                               WebFloatPoint(618, 298), WebFloatPoint(685, 436),
+                               WebPointerProperties::Button::Left, 1,
+                               WebInputEvent::Modifiers::LeftButtonDown,
+                               WebInputEvent::TimeStampForTesting);
+  mouseMoveEvent.setFrameScale(1);
   document().frame()->eventHandler().handleMouseMoveEvent(
-      mouseMoveEvent, Vector<PlatformMouseEvent>());
+      mouseMoveEvent, Vector<WebMouseEvent>());
 
   EXPECT_EQ(
       IntPoint(45, 44),
@@ -273,10 +287,11 @@ TEST_F(EventHandlerTest, sendContextMenuEventWithHover) {
       SelectionInDOMTree::Builder()
           .collapse(Position(document().body(), 0))
           .build());
-  PlatformMouseEvent mouseDownEvent(
-      IntPoint(0, 0), IntPoint(100, 200), WebPointerProperties::Button::Right,
-      PlatformEvent::MousePressed, 1, PlatformEvent::Modifiers::RightButtonDown,
-      TimeTicks::Now());
+  WebMouseEvent mouseDownEvent(
+      WebMouseEvent::MouseDown, WebFloatPoint(0, 0), WebFloatPoint(100, 200),
+      WebPointerProperties::Button::Right, 1,
+      PlatformEvent::Modifiers::RightButtonDown, TimeTicks::Now().InSeconds());
+  mouseDownEvent.setFrameScale(1);
   EXPECT_EQ(
       WebInputEventResult::HandledApplication,
       document().frame()->eventHandler().sendContextMenuEvent(mouseDownEvent));
@@ -387,18 +402,20 @@ TEST_F(EventHandlerTest, dragEndInNewDrag) {
       "<style>.box { width: 100px; height: 100px; display: block; }</style>"
       "<a class='box' href=''>Drag me</a>");
 
-  PlatformMouseEvent mouseDownEvent(
-      IntPoint(50, 50), IntPoint(50, 50), WebPointerProperties::Button::Left,
-      PlatformEvent::MousePressed, 1, PlatformEvent::Modifiers::LeftButtonDown,
-      TimeTicks::Now());
+  WebMouseEvent mouseDownEvent(
+      WebInputEvent::MouseDown, WebFloatPoint(50, 50), WebFloatPoint(50, 50),
+      WebPointerProperties::Button::Left, 1,
+      PlatformEvent::Modifiers::LeftButtonDown, TimeTicks::Now().InSeconds());
+  mouseDownEvent.setFrameScale(1);
   document().frame()->eventHandler().handleMousePressEvent(mouseDownEvent);
 
-  PlatformMouseEvent mouseMoveEvent(
-      IntPoint(51, 50), IntPoint(51, 50), WebPointerProperties::Button::Left,
-      PlatformEvent::MouseMoved, 1, PlatformEvent::Modifiers::LeftButtonDown,
-      TimeTicks::Now());
+  WebMouseEvent mouseMoveEvent(
+      WebInputEvent::MouseMove, WebFloatPoint(51, 50), WebFloatPoint(51, 50),
+      WebPointerProperties::Button::Left, 1,
+      PlatformEvent::Modifiers::LeftButtonDown, TimeTicks::Now().InSeconds());
+  mouseMoveEvent.setFrameScale(1);
   document().frame()->eventHandler().handleMouseMoveEvent(
-      mouseMoveEvent, Vector<PlatformMouseEvent>());
+      mouseMoveEvent, Vector<WebMouseEvent>());
 
   // This reproduces what might be the conditions of http://crbug.com/677916
   //
@@ -406,10 +423,11 @@ TEST_F(EventHandlerTest, dragEndInNewDrag) {
   // this contrived test. Given the current code, it is unclear how the
   // dragSourceEndedAt() call could occur before a drag operation is started.
 
-  PlatformMouseEvent mouseUpEvent(
-      IntPoint(100, 50), IntPoint(200, 250), WebPointerProperties::Button::Left,
-      PlatformEvent::MouseReleased, 1, static_cast<PlatformEvent::Modifiers>(0),
-      TimeTicks::Now());
+  WebMouseEvent mouseUpEvent(
+      WebInputEvent::MouseUp, WebFloatPoint(100, 50), WebFloatPoint(200, 250),
+      WebPointerProperties::Button::Left, 1,
+      static_cast<PlatformEvent::Modifiers>(0), TimeTicks::Now().InSeconds());
+  mouseUpEvent.setFrameScale(1);
   document().frame()->eventHandler().dragSourceEndedAt(mouseUpEvent,
                                                        DragOperationNone);
 
diff --git a/third_party/WebKit/Source/core/input/EventHandlingUtil.cpp b/third_party/WebKit/Source/core/input/EventHandlingUtil.cpp
index 908de11084e01b..4c8e0fb2ba5c5f 100644
--- a/third_party/WebKit/Source/core/input/EventHandlingUtil.cpp
+++ b/third_party/WebKit/Source/core/input/EventHandlingUtil.cpp
@@ -9,6 +9,7 @@
 #include "core/layout/api/LayoutViewItem.h"
 #include "core/paint/PaintLayer.h"
 #include "platform/scroll/ScrollableArea.h"
+#include "public/platform/WebMouseEvent.h"
 
 namespace blink {
 namespace EventHandlingUtil {
@@ -110,12 +111,14 @@ LayoutPoint contentPointFromRootFrame(LocalFrame* frame,
 MouseEventWithHitTestResults performMouseEventHitTest(
     LocalFrame* frame,
     const HitTestRequest& request,
-    const PlatformMouseEvent& mev) {
+    const WebMouseEvent& mev) {
   DCHECK(frame);
   DCHECK(frame->document());
 
   return frame->document()->performMouseEventHitTest(
-      request, contentPointFromRootFrame(frame, mev.position()), mev);
+      request, contentPointFromRootFrame(
+                   frame, flooredIntPoint(mev.positionInRootFrame())),
+      mev);
 }
 
 }  // namespace EventHandlingUtil
diff --git a/third_party/WebKit/Source/core/input/EventHandlingUtil.h b/third_party/WebKit/Source/core/input/EventHandlingUtil.h
index 558ae12dc89884..8e45b6bf6b6110 100644
--- a/third_party/WebKit/Source/core/input/EventHandlingUtil.h
+++ b/third_party/WebKit/Source/core/input/EventHandlingUtil.h
@@ -36,10 +36,9 @@ ContainerNode* parentForClickEvent(const Node&);
 LayoutPoint contentPointFromRootFrame(LocalFrame*,
                                       const IntPoint& pointInRootFrame);
 
-MouseEventWithHitTestResults performMouseEventHitTest(
-    LocalFrame*,
-    const HitTestRequest&,
-    const PlatformMouseEvent&);
+MouseEventWithHitTestResults performMouseEventHitTest(LocalFrame*,
+                                                      const HitTestRequest&,
+                                                      const WebMouseEvent&);
 
 }  // namespace EventHandlingUtil
 
diff --git a/third_party/WebKit/Source/core/input/GestureManager.cpp b/third_party/WebKit/Source/core/input/GestureManager.cpp
index 780be37131a5aa..5646057fc0f7b8 100644
--- a/third_party/WebKit/Source/core/input/GestureManager.cpp
+++ b/third_party/WebKit/Source/core/input/GestureManager.cpp
@@ -150,15 +150,16 @@ WebInputEventResult GestureManager::handleGestureTap(
   const unsigned modifiers = gestureEvent.modifiers();
 
   if (!m_suppressMouseEventsFromGestures) {
-    PlatformMouseEvent fakeMouseMove(
-        gestureEvent, WebPointerProperties::Button::NoButton,
-        PlatformEvent::MouseMoved,
-        /* clickCount */ 0, static_cast<PlatformEvent::Modifiers>(modifiers),
-        PlatformMouseEvent::FromTouch,
-        TimeTicks::FromSeconds(gestureEvent.timeStampSeconds()),
-        WebPointerProperties::PointerType::Mouse);
+    WebMouseEvent fakeMouseMove(
+        WebInputEvent::MouseMove, gestureEvent,
+        WebPointerProperties::Button::NoButton,
+        /* clickCount */ 0,
+        static_cast<PlatformEvent::Modifiers>(
+            modifiers | WebInputEvent::Modifiers::IsCompatibilityEventForTouch),
+        gestureEvent.timeStampSeconds());
     m_mouseEventManager->setMousePositionAndDispatchMouseEvent(
-        currentHitTest.innerNode(), EventTypeNames::mousemove, fakeMouseMove);
+        currentHitTest.innerNode(), currentHitTest.canvasRegionId(),
+        EventTypeNames::mousemove, fakeMouseMove);
   }
 
   // Do a new hit-test in case the mousemove event changed the DOM.
@@ -192,14 +193,13 @@ WebInputEventResult GestureManager::handleGestureTap(
 
   m_mouseEventManager->setClickNode(tappedNonTextNode);
 
-  PlatformMouseEvent fakeMouseDown(
-      gestureEvent, WebPointerProperties::Button::Left,
-      PlatformEvent::MousePressed, gestureEvent.tapCount(),
-      static_cast<PlatformEvent::Modifiers>(modifiers |
-                                            PlatformEvent::LeftButtonDown),
-      PlatformMouseEvent::FromTouch,
-      TimeTicks::FromSeconds(gestureEvent.timeStampSeconds()),
-      WebPointerProperties::PointerType::Mouse);
+  WebMouseEvent fakeMouseDown(
+      WebInputEvent::MouseDown, gestureEvent,
+      WebPointerProperties::Button::Left, gestureEvent.tapCount(),
+      static_cast<PlatformEvent::Modifiers>(
+          modifiers | WebInputEvent::Modifiers::LeftButtonDown |
+          WebInputEvent::Modifiers::IsCompatibilityEventForTouch),
+      gestureEvent.timeStampSeconds());
 
   // TODO(mustaq): We suppress MEs plus all it's side effects. What would that
   // mean for for TEs?  What's the right balance here? crbug.com/617255
@@ -210,8 +210,8 @@ WebInputEventResult GestureManager::handleGestureTap(
 
     mouseDownEventResult =
         m_mouseEventManager->setMousePositionAndDispatchMouseEvent(
-            currentHitTest.innerNode(), EventTypeNames::mousedown,
-            fakeMouseDown);
+            currentHitTest.innerNode(), currentHitTest.canvasRegionId(),
+            EventTypeNames::mousedown, fakeMouseDown);
     m_selectionController->initializeSelectionState();
     if (mouseDownEventResult == WebInputEventResult::NotHandled)
       mouseDownEventResult = m_mouseEventManager->handleMouseFocus(
@@ -240,19 +240,18 @@ WebInputEventResult GestureManager::handleGestureTap(
         m_frame, adjustedPoint, hitType);
   }
 
-  PlatformMouseEvent fakeMouseUp(
-      gestureEvent, WebPointerProperties::Button::Left,
-      PlatformEvent::MouseReleased, gestureEvent.tapCount(),
-      static_cast<PlatformEvent::Modifiers>(modifiers),
-      PlatformMouseEvent::FromTouch,
-      TimeTicks::FromSeconds(gestureEvent.timeStampSeconds()),
-      WebPointerProperties::PointerType::Mouse);
+  WebMouseEvent fakeMouseUp(
+      WebInputEvent::MouseUp, gestureEvent, WebPointerProperties::Button::Left,
+      gestureEvent.tapCount(),
+      static_cast<PlatformEvent::Modifiers>(
+          modifiers | WebInputEvent::Modifiers::IsCompatibilityEventForTouch),
+      gestureEvent.timeStampSeconds());
   WebInputEventResult mouseUpEventResult =
       m_suppressMouseEventsFromGestures
           ? WebInputEventResult::HandledSuppressed
           : m_mouseEventManager->setMousePositionAndDispatchMouseEvent(
-                currentHitTest.innerNode(), EventTypeNames::mouseup,
-                fakeMouseUp);
+                currentHitTest.innerNode(), currentHitTest.canvasRegionId(),
+                EventTypeNames::mouseup, fakeMouseUp);
 
   WebInputEventResult clickEventResult = WebInputEventResult::NotHandled;
   if (tappedNonTextNode) {
@@ -268,7 +267,7 @@ WebInputEventResult GestureManager::handleGestureTap(
           *tappedNonTextNode, EventHandlingUtil::parentForClickEvent);
       clickEventResult =
           m_mouseEventManager->setMousePositionAndDispatchMouseEvent(
-              clickTargetNode, EventTypeNames::click, fakeMouseUp);
+              clickTargetNode, String(), EventTypeNames::click, fakeMouseUp);
     }
     m_mouseEventManager->setClickNode(nullptr);
   }
@@ -361,30 +360,31 @@ WebInputEventResult GestureManager::sendContextMenuEventForGesture(
   unsigned modifiers = gestureEvent.modifiers();
 
   if (!m_suppressMouseEventsFromGestures) {
-    // Send MouseMoved event prior to handling (https://crbug.com/485290).
-    PlatformMouseEvent fakeMouseMove(
-        gestureEvent, WebPointerProperties::Button::NoButton,
-        PlatformEvent::MouseMoved,
-        /* clickCount */ 0, static_cast<PlatformEvent::Modifiers>(modifiers),
-        PlatformMouseEvent::FromTouch,
-        TimeTicks::FromSeconds(gestureEvent.timeStampSeconds()),
-        WebPointerProperties::PointerType::Mouse);
+    // Send MouseMove event prior to handling (https://crbug.com/485290).
+    WebMouseEvent fakeMouseMove(
+        WebInputEvent::MouseMove, gestureEvent,
+        WebPointerProperties::Button::NoButton,
+        /* clickCount */ 0,
+        static_cast<PlatformEvent::Modifiers>(
+            modifiers | WebInputEvent::IsCompatibilityEventForTouch),
+        gestureEvent.timeStampSeconds());
     m_mouseEventManager->setMousePositionAndDispatchMouseEvent(
-        targetedEvent.hitTestResult().innerNode(), EventTypeNames::mousemove,
+        targetedEvent.hitTestResult().innerNode(),
+        targetedEvent.canvasRegionId(), EventTypeNames::mousemove,
         fakeMouseMove);
   }
 
-  PlatformEvent::EventType eventType = PlatformEvent::MousePressed;
+  WebInputEvent::Type eventType = WebInputEvent::MouseDown;
   if (m_frame->settings() && m_frame->settings()->getShowContextMenuOnMouseUp())
-    eventType = PlatformEvent::MouseReleased;
+    eventType = WebInputEvent::MouseUp;
 
-  PlatformMouseEvent mouseEvent(
-      gestureEvent, WebPointerProperties::Button::Right, eventType,
+  WebMouseEvent mouseEvent(
+      eventType, gestureEvent, WebPointerProperties::Button::Right,
       /* clickCount */ 1,
       static_cast<PlatformEvent::Modifiers>(
-          modifiers | PlatformEvent::Modifiers::RightButtonDown),
-      PlatformMouseEvent::FromTouch, TimeTicks::Now(),
-      WebPointerProperties::PointerType::Mouse);
+          modifiers | PlatformEvent::Modifiers::RightButtonDown |
+          WebInputEvent::IsCompatibilityEventForTouch),
+      gestureEvent.timeStampSeconds());
 
   if (!m_suppressMouseEventsFromGestures && m_frame->view()) {
     HitTestRequest request(HitTestRequest::Active);
diff --git a/third_party/WebKit/Source/core/input/MouseEventManager.cpp b/third_party/WebKit/Source/core/input/MouseEventManager.cpp
index bb2943116f4784..aaca3de4a6922a 100644
--- a/third_party/WebKit/Source/core/input/MouseEventManager.cpp
+++ b/third_party/WebKit/Source/core/input/MouseEventManager.cpp
@@ -35,25 +35,21 @@ namespace blink {
 
 namespace {
 
-PlatformMouseEvent mouseEventWithRegion(Node* node,
-                                        const PlatformMouseEvent& mouseEvent) {
+String canvasRegionId(Node* node, const WebMouseEvent& mouseEvent) {
   if (!node->isElementNode())
-    return mouseEvent;
+    return String();
 
   Element* element = toElement(node);
   if (!element->isInCanvasSubtree())
-    return mouseEvent;
+    return String();
 
   HTMLCanvasElement* canvas =
       Traversal<HTMLCanvasElement>::firstAncestorOrSelf(*element);
   // In this case, the event target is canvas and mouse rerouting doesn't
   // happen.
   if (canvas == element)
-    return mouseEvent;
-  String region = canvas->getIdFromControl(element);
-  PlatformMouseEvent newMouseEvent = mouseEvent;
-  newMouseEvent.setRegion(region);
-  return newMouseEvent;
+    return String();
+  return canvas->getIdFromControl(element);
 }
 
 // The amount of time to wait before sending a fake mouse event triggered
@@ -100,7 +96,7 @@ void MouseEventManager::clear() {
   m_clickNode = nullptr;
   m_mouseDownPos = IntPoint();
   m_mouseDownTimestamp = TimeTicks();
-  m_mouseDown = PlatformMouseEvent();
+  m_mouseDown = WebMouseEvent();
   m_svgPan = false;
   m_dragStartPos = LayoutPoint();
   m_fakeMouseMoveEventTimer.stop();
@@ -118,46 +114,45 @@ DEFINE_TRACE(MouseEventManager) {
 }
 
 MouseEventManager::MouseEventBoundaryEventDispatcher::
-    MouseEventBoundaryEventDispatcher(
-        MouseEventManager* mouseEventManager,
-        const PlatformMouseEvent* platformMouseEvent,
-        EventTarget* exitedTarget)
+    MouseEventBoundaryEventDispatcher(MouseEventManager* mouseEventManager,
+                                      const WebMouseEvent* webMouseEvent,
+                                      EventTarget* exitedTarget,
+                                      const String& canvasRegionId)
     : m_mouseEventManager(mouseEventManager),
-      m_platformMouseEvent(platformMouseEvent),
-      m_exitedTarget(exitedTarget) {}
+      m_webMouseEvent(webMouseEvent),
+      m_exitedTarget(exitedTarget),
+      m_canvasRegionId(canvasRegionId) {}
 
 void MouseEventManager::MouseEventBoundaryEventDispatcher::dispatchOut(
     EventTarget* target,
     EventTarget* relatedTarget) {
-  dispatch(
-      target, relatedTarget, EventTypeNames::mouseout,
-      mouseEventWithRegion(m_exitedTarget->toNode(), *m_platformMouseEvent),
-      false);
+  dispatch(target, relatedTarget, EventTypeNames::mouseout,
+           canvasRegionId(m_exitedTarget->toNode(), *m_webMouseEvent),
+           *m_webMouseEvent, false);
 }
 
 void MouseEventManager::MouseEventBoundaryEventDispatcher::dispatchOver(
     EventTarget* target,
     EventTarget* relatedTarget) {
-  dispatch(target, relatedTarget, EventTypeNames::mouseover,
-           *m_platformMouseEvent, false);
+  dispatch(target, relatedTarget, EventTypeNames::mouseover, m_canvasRegionId,
+           *m_webMouseEvent, false);
 }
 
 void MouseEventManager::MouseEventBoundaryEventDispatcher::dispatchLeave(
     EventTarget* target,
     EventTarget* relatedTarget,
     bool checkForListener) {
-  dispatch(
-      target, relatedTarget, EventTypeNames::mouseleave,
-      mouseEventWithRegion(m_exitedTarget->toNode(), *m_platformMouseEvent),
-      checkForListener);
+  dispatch(target, relatedTarget, EventTypeNames::mouseleave,
+           canvasRegionId(m_exitedTarget->toNode(), *m_webMouseEvent),
+           *m_webMouseEvent, checkForListener);
 }
 
 void MouseEventManager::MouseEventBoundaryEventDispatcher::dispatchEnter(
     EventTarget* target,
     EventTarget* relatedTarget,
     bool checkForListener) {
-  dispatch(target, relatedTarget, EventTypeNames::mouseenter,
-           *m_platformMouseEvent, checkForListener);
+  dispatch(target, relatedTarget, EventTypeNames::mouseenter, m_canvasRegionId,
+           *m_webMouseEvent, checkForListener);
 }
 
 AtomicString
@@ -174,25 +169,28 @@ void MouseEventManager::MouseEventBoundaryEventDispatcher::dispatch(
     EventTarget* target,
     EventTarget* relatedTarget,
     const AtomicString& type,
-    const PlatformMouseEvent& platformMouseEvent,
+    const String& canvasRegionId,
+    const WebMouseEvent& webMouseEvent,
     bool checkForListener) {
-  m_mouseEventManager->dispatchMouseEvent(target, type, platformMouseEvent,
-                                          relatedTarget, checkForListener);
+  m_mouseEventManager->dispatchMouseEvent(target, type, webMouseEvent,
+                                          canvasRegionId, relatedTarget,
+                                          checkForListener);
 }
 
-void MouseEventManager::sendBoundaryEvents(
-    EventTarget* exitedTarget,
-    EventTarget* enteredTarget,
-    const PlatformMouseEvent& mousePlatformEvent) {
+void MouseEventManager::sendBoundaryEvents(EventTarget* exitedTarget,
+                                           EventTarget* enteredTarget,
+                                           const String& canvasRegionId,
+                                           const WebMouseEvent& mouseEvent) {
   MouseEventBoundaryEventDispatcher boundaryEventDispatcher(
-      this, &mousePlatformEvent, exitedTarget);
+      this, &mouseEvent, exitedTarget, canvasRegionId);
   boundaryEventDispatcher.sendBoundaryEvents(exitedTarget, enteredTarget);
 }
 
 WebInputEventResult MouseEventManager::dispatchMouseEvent(
     EventTarget* target,
     const AtomicString& mouseEventType,
-    const PlatformMouseEvent& mouseEvent,
+    const WebMouseEvent& mouseEvent,
+    const String& canvasRegionId,
     EventTarget* relatedTarget,
     bool checkForListener) {
   if (target && target->toNode() &&
@@ -206,9 +204,10 @@ WebInputEventResult MouseEventManager::dispatchMouseEvent(
         mouseEventType == EventTypeNames::dblclick) {
       clickCount = m_clickCount;
     }
-    MouseEvent* event = MouseEvent::create(
-        mouseEventType, targetNode->document().domWindow(), mouseEvent,
-        clickCount, relatedTarget ? relatedTarget->toNode() : nullptr);
+    MouseEvent* event =
+        MouseEvent::create(mouseEventType, targetNode->document().domWindow(),
+                           mouseEvent, clickCount, canvasRegionId,
+                           relatedTarget ? relatedTarget->toNode() : nullptr);
     DispatchEventResult dispatchResult = target->dispatchEvent(event);
     return EventHandlingUtil::toWebInputEventResult(dispatchResult);
   }
@@ -217,32 +216,32 @@ WebInputEventResult MouseEventManager::dispatchMouseEvent(
 
 WebInputEventResult MouseEventManager::setMousePositionAndDispatchMouseEvent(
     Node* targetNode,
+    const String& canvasRegionId,
     const AtomicString& eventType,
-    const PlatformMouseEvent& platformMouseEvent) {
+    const WebMouseEvent& webMouseEvent) {
   // If the target node is a text node, dispatch on the parent node.
   if (targetNode && targetNode->isTextNode())
     targetNode = FlatTreeTraversal::parent(*targetNode);
 
-  setNodeUnderMouse(targetNode, platformMouseEvent);
+  setNodeUnderMouse(targetNode, canvasRegionId, webMouseEvent);
 
-  return dispatchMouseEvent(m_nodeUnderMouse, eventType, platformMouseEvent,
-                            nullptr);
+  return dispatchMouseEvent(m_nodeUnderMouse, eventType, webMouseEvent,
+                            canvasRegionId, nullptr);
 }
 
 WebInputEventResult MouseEventManager::dispatchMouseClickIfNeeded(
     const MouseEventWithHitTestResults& mev) {
   // We only prevent click event when the click may cause contextmenu to popup.
   // However, we always send auxclick.
-  bool contextMenuEvent = !RuntimeEnabledFeatures::auxclickEnabled() &&
-                          mev.event().pointerProperties().button ==
-                              WebPointerProperties::Button::Right;
+  bool contextMenuEvent =
+      !RuntimeEnabledFeatures::auxclickEnabled() &&
+      mev.event().button == WebPointerProperties::Button::Right;
 #if OS(MACOSX)
   // FIXME: The Mac port achieves the same behavior by checking whether the
   // context menu is currently open in WebPage::mouseEvent(). Consider merging
   // the implementations.
-  if (mev.event().pointerProperties().button ==
-          WebPointerProperties::Button::Left &&
-      mev.event().getModifiers() & PlatformEvent::CtrlKey)
+  if (mev.event().button == WebPointerProperties::Button::Left &&
+      mev.event().modifiers() & WebInputEvent::Modifiers::ControlKey)
     contextMenuEvent = true;
 #endif
 
@@ -269,12 +268,12 @@ WebInputEventResult MouseEventManager::dispatchMouseClickIfNeeded(
     }
     if (clickTargetNode) {
       clickEventResult = dispatchMouseEvent(
-          clickTargetNode, !RuntimeEnabledFeatures::auxclickEnabled() ||
-                                   (mev.event().pointerProperties().button ==
-                                    WebPointerProperties::Button::Left)
-                               ? EventTypeNames::click
-                               : EventTypeNames::auxclick,
-          mev.event(), nullptr);
+          clickTargetNode,
+          !RuntimeEnabledFeatures::auxclickEnabled() ||
+                  (mev.event().button == WebPointerProperties::Button::Left)
+              ? EventTypeNames::click
+              : EventTypeNames::auxclick,
+          mev.event(), mev.canvasRegionId(), nullptr);
     }
   }
   return clickEventResult;
@@ -300,14 +299,17 @@ void MouseEventManager::fakeMouseMoveEventTimerFired(TimerBase* timer) {
   if (!m_frame->page()->isCursorVisible())
     return;
 
-  PlatformMouseEvent fakeMouseMoveEvent(
-      m_lastKnownMousePosition, m_lastKnownMouseGlobalPosition,
-      WebPointerProperties::Button::NoButton, PlatformEvent::MouseMoved, 0,
-      static_cast<PlatformEvent::Modifiers>(
-          KeyboardEventManager::getCurrentModifierState()),
-      PlatformMouseEvent::RealOrIndistinguishable, TimeTicks::Now(),
-      WebPointerProperties::PointerType::Mouse);
-  Vector<PlatformMouseEvent> coalescedEvents;
+  WebMouseEvent fakeMouseMoveEvent(
+      WebInputEvent::MouseMove,
+      WebFloatPoint(m_lastKnownMousePosition.x(), m_lastKnownMousePosition.y()),
+      WebFloatPoint(m_lastKnownMouseGlobalPosition.x(),
+                    m_lastKnownMouseGlobalPosition.y()),
+      WebPointerProperties::Button::NoButton, 0,
+      KeyboardEventManager::getCurrentModifierState(),
+      TimeTicks::Now().InSeconds());
+  // TODO(dtapuska): Update m_lastKnowMousePosition to be viewport coordinates.
+  fakeMouseMoveEvent.setFrameScale(1);
+  Vector<WebMouseEvent> coalescedEvents;
   m_frame->eventHandler().handleMouseMoveEvent(fakeMouseMoveEvent,
                                                coalescedEvents);
 }
@@ -316,9 +318,9 @@ void MouseEventManager::cancelFakeMouseMoveEvent() {
   m_fakeMouseMoveEventTimer.stop();
 }
 
-void MouseEventManager::setNodeUnderMouse(
-    Node* target,
-    const PlatformMouseEvent& platformMouseEvent) {
+void MouseEventManager::setNodeUnderMouse(Node* target,
+                                          const String& canvasRegionId,
+                                          const WebMouseEvent& webMouseEvent) {
   Node* lastNodeUnderMouse = m_nodeUnderMouse;
   m_nodeUnderMouse = target;
 
@@ -367,7 +369,8 @@ void MouseEventManager::setNodeUnderMouse(
     lastNodeUnderMouse = nullptr;
   }
 
-  sendBoundaryEvents(lastNodeUnderMouse, m_nodeUnderMouse, platformMouseEvent);
+  sendBoundaryEvents(lastNodeUnderMouse, m_nodeUnderMouse, canvasRegionId,
+                     webMouseEvent);
 }
 
 void MouseEventManager::nodeChildrenWillBeRemoved(ContainerNode& container) {
@@ -493,17 +496,18 @@ bool MouseEventManager::slideFocusOnShadowHostIfNecessary(
 }
 
 void MouseEventManager::handleMousePressEventUpdateStates(
-    const PlatformMouseEvent& mouseEvent) {
+    const WebMouseEvent& mouseEvent) {
   cancelFakeMouseMoveEvent();
   m_mousePressed = true;
   m_capturesDragging = true;
   setLastKnownMousePosition(mouseEvent);
   m_mouseDownMayStartDrag = false;
   m_mouseDownMayStartAutoscroll = false;
-  m_mouseDownTimestamp = mouseEvent.timestamp();
+  m_mouseDownTimestamp = TimeTicks::FromSeconds(mouseEvent.timeStampSeconds());
 
   if (FrameView* view = m_frame->view()) {
-    m_mouseDownPos = view->rootFrameToContents(mouseEvent.position());
+    m_mouseDownPos = view->rootFrameToContents(
+        flooredIntPoint(mouseEvent.positionInRootFrame()));
   } else {
     invalidateClick();
   }
@@ -517,11 +521,10 @@ IntPoint MouseEventManager::lastKnownMousePosition() {
   return m_lastKnownMousePosition;
 }
 
-void MouseEventManager::setLastKnownMousePosition(
-    const PlatformMouseEvent& event) {
+void MouseEventManager::setLastKnownMousePosition(const WebMouseEvent& event) {
   m_isMousePositionUnknown = false;
-  m_lastKnownMousePosition = event.position();
-  m_lastKnownMouseGlobalPosition = event.globalPosition();
+  m_lastKnownMousePosition = flooredIntPoint(event.positionInRootFrame());
+  m_lastKnownMouseGlobalPosition = IntPoint(event.globalX, event.globalY);
 }
 
 void MouseEventManager::dispatchFakeMouseMoveEventSoon() {
@@ -561,11 +564,12 @@ WebInputEventResult MouseEventManager::handleMousePressEvent(
   m_frame->document()->updateStyleAndLayoutIgnorePendingStylesheets();
 
   if (FrameView* frameView = m_frame->view()) {
-    if (frameView->isPointInScrollbarCorner(event.event().position()))
+    if (frameView->isPointInScrollbarCorner(
+            flooredIntPoint(event.event().positionInRootFrame())))
       return WebInputEventResult::NotHandled;
   }
 
-  bool singleClick = event.event().clickCount() <= 1;
+  bool singleClick = event.event().clickCount <= 1;
 
   m_mouseDownMayStartDrag =
       singleClick && !isLinkSelection(event) && !isExtendingSelection(event);
@@ -576,10 +580,12 @@ WebInputEventResult MouseEventManager::handleMousePressEvent(
 
   if (m_frame->document()->isSVGDocument() &&
       m_frame->document()->accessSVGExtensions().zoomAndPanEnabled()) {
-    if (event.event().shiftKey() && singleClick) {
+    if ((event.event().modifiers() & WebInputEvent::Modifiers::ShiftKey) &&
+        singleClick) {
       m_svgPan = true;
       m_frame->document()->accessSVGExtensions().startPan(
-          m_frame->view()->rootFrameToContents(event.event().position()));
+          m_frame->view()->rootFrameToContents(
+              flooredIntPoint(event.event().positionInRootFrame())));
       return WebInputEventResult::HandledSystem;
     }
   }
@@ -593,16 +599,16 @@ WebInputEventResult MouseEventManager::handleMousePressEvent(
 
   m_mousePressNode = innerNode;
   m_frame->document()->setSequentialFocusNavigationStartingPoint(innerNode);
-  m_dragStartPos = event.event().position();
+  m_dragStartPos = flooredIntPoint(event.event().positionInRootFrame());
 
   bool swallowEvent = false;
   m_mousePressed = true;
 
-  if (event.event().clickCount() == 2) {
+  if (event.event().clickCount == 2) {
     swallowEvent = m_frame->eventHandler()
                        .selectionController()
                        .handleMousePressEventDoubleClick(event);
-  } else if (event.event().clickCount() >= 3) {
+  } else if (event.event().clickCount >= 3) {
     swallowEvent = m_frame->eventHandler()
                        .selectionController()
                        .handleMousePressEventTripleClick(event);
@@ -647,30 +653,28 @@ bool MouseEventManager::handleDragDropIfPossible(
 
     // TODO(mustaq): Suppressing long-tap MouseEvents could break
     // drag-drop. Will do separately because of the risk. crbug.com/606938.
-    PlatformMouseEvent mouseDownEvent(
-        gestureEvent, WebPointerProperties::Button::Left,
-        PlatformEvent::MousePressed, 1,
-        static_cast<PlatformEvent::Modifiers>(modifiers |
-                                              PlatformEvent::LeftButtonDown),
-        PlatformMouseEvent::FromTouch, TimeTicks::Now(),
-        WebPointerProperties::PointerType::Mouse);
+    WebMouseEvent mouseDownEvent(
+        WebInputEvent::MouseDown, gestureEvent,
+        WebPointerProperties::Button::Left, 1,
+        modifiers | WebInputEvent::Modifiers::LeftButtonDown |
+            WebInputEvent::Modifiers::IsCompatibilityEventForTouch,
+        TimeTicks::Now().InSeconds());
     m_mouseDown = mouseDownEvent;
 
-    PlatformMouseEvent mouseDragEvent(
-        gestureEvent, WebPointerProperties::Button::Left,
-        PlatformEvent::MouseMoved, 1,
-        static_cast<PlatformEvent::Modifiers>(modifiers |
-                                              PlatformEvent::LeftButtonDown),
-        PlatformMouseEvent::FromTouch, TimeTicks::Now(),
-        WebPointerProperties::PointerType::Mouse);
+    WebMouseEvent mouseDragEvent(
+        WebInputEvent::MouseMove, gestureEvent,
+        WebPointerProperties::Button::Left, 1,
+        modifiers | WebInputEvent::Modifiers::LeftButtonDown |
+            WebInputEvent::Modifiers::IsCompatibilityEventForTouch,
+        TimeTicks::Now().InSeconds());
     HitTestRequest request(HitTestRequest::ReadOnly);
     MouseEventWithHitTestResults mev =
         EventHandlingUtil::performMouseEventHitTest(m_frame, request,
                                                     mouseDragEvent);
     m_mouseDownMayStartDrag = true;
     dragState().m_dragSrc = nullptr;
-    m_mouseDownPos =
-        m_frame->view()->rootFrameToContents(mouseDragEvent.position());
+    m_mouseDownPos = m_frame->view()->rootFrameToContents(
+        flooredIntPoint(mouseDragEvent.positionInRootFrame()));
     return handleDrag(mev, DragInitiator::Touch);
   }
   return false;
@@ -701,8 +705,7 @@ WebInputEventResult MouseEventManager::handleMouseDraggedEvent(
   //    that ends as a result of a mouse release does not send a mouse release
   //    event. As a result, m_mousePressed also ends up remaining true until
   //    the next mouse release event seen by the EventHandler.
-  if (event.event().pointerProperties().button !=
-      WebPointerProperties::Button::Left)
+  if (event.event().button != WebPointerProperties::Button::Left)
     m_mousePressed = false;
 
   if (!m_mousePressed)
@@ -751,7 +754,7 @@ WebInputEventResult MouseEventManager::handleMouseDraggedEvent(
 
 bool MouseEventManager::handleDrag(const MouseEventWithHitTestResults& event,
                                    DragInitiator initiator) {
-  DCHECK(event.event().type() == PlatformEvent::MouseMoved);
+  DCHECK(event.event().type() == WebInputEvent::MouseMove);
   // Callers must protect the reference to FrameView, since this function may
   // dispatch DOM events, causing page/FrameView to go away.
   DCHECK(m_frame);
@@ -766,7 +769,9 @@ bool MouseEventManager::handleDrag(const MouseEventWithHitTestResults& event,
     Node* node = result.innerNode();
     if (node) {
       DragController::SelectionDragPolicy selectionDragPolicy =
-          event.event().timestamp() - m_mouseDownTimestamp < kTextDragDelay
+          TimeTicks::FromSeconds(event.event().timeStampSeconds()) -
+                      m_mouseDownTimestamp <
+                  kTextDragDelay
               ? DragController::DelayedSelectionDragResolution
               : DragController::ImmediateSelectionDragResolution;
       dragState().m_dragSrc = m_frame->page()->dragController().draggableNode(
@@ -794,7 +799,8 @@ bool MouseEventManager::handleDrag(const MouseEventWithHitTestResults& event,
   m_frame->view()->setCursor(pointerCursor());
 
   if (initiator == DragInitiator::Mouse &&
-      !dragThresholdExceeded(event.event().position())) {
+      !dragThresholdExceeded(
+          flooredIntPoint(event.event().positionInRootFrame()))) {
     dragState().m_dragSrc = nullptr;
     return true;
   }
@@ -867,7 +873,7 @@ bool MouseEventManager::tryStartDrag(
 // eventhandler canceled.
 WebInputEventResult MouseEventManager::dispatchDragSrcEvent(
     const AtomicString& eventType,
-    const PlatformMouseEvent& event) {
+    const WebMouseEvent& event) {
   return dispatchDragEvent(eventType, dragState().m_dragSrc.get(), event,
                            dragState().m_dragDataTransfer.get());
 }
@@ -875,7 +881,7 @@ WebInputEventResult MouseEventManager::dispatchDragSrcEvent(
 WebInputEventResult MouseEventManager::dispatchDragEvent(
     const AtomicString& eventType,
     Node* dragTarget,
-    const PlatformMouseEvent& event,
+    const WebMouseEvent& event,
     DataTransfer* dataTransfer) {
   FrameView* view = m_frame->view();
 
@@ -886,13 +892,16 @@ WebInputEventResult MouseEventManager::dispatchDragEvent(
   const bool cancelable = eventType != EventTypeNames::dragleave &&
                           eventType != EventTypeNames::dragend;
 
+  IntPoint position = flooredIntPoint(event.positionInRootFrame());
+  IntPoint movement = flooredIntPoint(event.movementInRootFrame());
   DragEvent* me = DragEvent::create(
       eventType, true, cancelable, m_frame->document()->domWindow(), 0,
-      event.globalPosition().x(), event.globalPosition().y(),
-      event.position().x(), event.position().y(), event.movementDelta().x(),
-      event.movementDelta().y(), event.getModifiers(), 0,
-      MouseEvent::platformModifiersToButtons(event.getModifiers()), nullptr,
-      event.timestamp(), dataTransfer, event.getSyntheticEventType());
+      event.globalX, event.globalY, position.x(), position.y(), movement.x(),
+      movement.y(), static_cast<PlatformEvent::Modifiers>(event.modifiers()), 0,
+      MouseEvent::platformModifiersToButtons(event.modifiers()), nullptr,
+      TimeTicks::FromSeconds(event.timeStampSeconds()), dataTransfer,
+      event.fromTouch() ? MouseEvent::FromTouch
+                        : MouseEvent::RealOrIndistinguishable);
 
   return EventHandlingUtil::toWebInputEventResult(
       dragTarget->dispatchEvent(me));
@@ -905,7 +914,7 @@ void MouseEventManager::clearDragDataTransfer() {
   }
 }
 
-void MouseEventManager::dragSourceEndedAt(const PlatformMouseEvent& event,
+void MouseEventManager::dragSourceEndedAt(const WebMouseEvent& event,
                                           DragOperation operation) {
   if (dragState().m_dragSrc) {
     dragState().m_dragDataTransfer->setDestinationOperation(operation);
diff --git a/third_party/WebKit/Source/core/input/MouseEventManager.h b/third_party/WebKit/Source/core/input/MouseEventManager.h
index aa8640a042e6c2..0628dfb560b3d6 100644
--- a/third_party/WebKit/Source/core/input/MouseEventManager.h
+++ b/third_party/WebKit/Source/core/input/MouseEventManager.h
@@ -10,9 +10,9 @@
 #include "core/input/BoundaryEventDispatcher.h"
 #include "core/page/DragActions.h"
 #include "core/page/EventWithHitTestResults.h"
-#include "platform/PlatformMouseEvent.h"
 #include "platform/Timer.h"
 #include "public/platform/WebInputEventResult.h"
+#include "public/platform/WebMouseEvent.h"
 #include "wtf/Allocator.h"
 #include "wtf/Time.h"
 
@@ -45,23 +45,25 @@ class CORE_EXPORT MouseEventManager final
 
   WebInputEventResult dispatchMouseEvent(EventTarget*,
                                          const AtomicString&,
-                                         const PlatformMouseEvent&,
+                                         const WebMouseEvent&,
+                                         const String& canvasRegionId,
                                          EventTarget* relatedTarget,
                                          bool checkForListener = false);
 
   WebInputEventResult setMousePositionAndDispatchMouseEvent(
       Node* targetNode,
+      const String& canvasRegionId,
       const AtomicString& eventType,
-      const PlatformMouseEvent&);
+      const WebMouseEvent&);
 
   WebInputEventResult dispatchMouseClickIfNeeded(
       const MouseEventWithHitTestResults&);
 
   WebInputEventResult dispatchDragSrcEvent(const AtomicString& eventType,
-                                           const PlatformMouseEvent&);
+                                           const WebMouseEvent&);
   WebInputEventResult dispatchDragEvent(const AtomicString& eventType,
                                         Node* target,
-                                        const PlatformMouseEvent&,
+                                        const WebMouseEvent&,
                                         DataTransfer*);
 
   // Resets the internal state of this object.
@@ -69,9 +71,12 @@ class CORE_EXPORT MouseEventManager final
 
   void sendBoundaryEvents(EventTarget* exitedTarget,
                           EventTarget* enteredTarget,
-                          const PlatformMouseEvent& mousePlatformEvent);
+                          const String& canvasRegionId,
+                          const WebMouseEvent&);
 
-  void setNodeUnderMouse(Node*, const PlatformMouseEvent&);
+  void setNodeUnderMouse(Node*,
+                         const String& canvasRegionId,
+                         const WebMouseEvent&);
 
   WebInputEventResult handleMouseFocus(
       const HitTestResult&,
@@ -83,7 +88,7 @@ class CORE_EXPORT MouseEventManager final
   void dispatchFakeMouseMoveEventSoon();
   void dispatchFakeMouseMoveEventSoonInQuad(const FloatQuad&);
 
-  void setLastKnownMousePosition(const PlatformMouseEvent&);
+  void setLastKnownMousePosition(const WebMouseEvent&);
 
   bool handleDragDropIfPossible(const GestureEventWithHitTestResults&);
 
@@ -103,11 +108,11 @@ class CORE_EXPORT MouseEventManager final
   // drag heuristics.
   void clearDragHeuristicState();
 
-  void dragSourceEndedAt(const PlatformMouseEvent&, DragOperation);
+  void dragSourceEndedAt(const WebMouseEvent&, DragOperation);
 
   void updateSelectionForMouseDrag();
 
-  void handleMousePressEventUpdateStates(const PlatformMouseEvent&);
+  void handleMousePressEventUpdateStates(const WebMouseEvent&);
 
   // Returns whether pan is handled and resets the state on release.
   bool handleSvgPanIfNeeded(bool isReleaseEvent);
@@ -144,8 +149,9 @@ class CORE_EXPORT MouseEventManager final
 
    public:
     MouseEventBoundaryEventDispatcher(MouseEventManager*,
-                                      const PlatformMouseEvent*,
-                                      EventTarget* exitedTarget);
+                                      const WebMouseEvent*,
+                                      EventTarget* exitedTarget,
+                                      const String& canvasRegionId);
 
    protected:
     void dispatchOut(EventTarget*, EventTarget* relatedTarget) override;
@@ -163,11 +169,13 @@ class CORE_EXPORT MouseEventManager final
     void dispatch(EventTarget*,
                   EventTarget* relatedTarget,
                   const AtomicString&,
-                  const PlatformMouseEvent&,
+                  const String& canvasRegionId,
+                  const WebMouseEvent&,
                   bool checkForListener);
     Member<MouseEventManager> m_mouseEventManager;
-    const PlatformMouseEvent* m_platformMouseEvent;
+    const WebMouseEvent* m_webMouseEvent;
     Member<EventTarget> m_exitedTarget;
+    String m_canvasRegionId;
   };
 
   // If the given element is a shadow host and its root has delegatesFocus=false
@@ -218,7 +226,7 @@ class CORE_EXPORT MouseEventManager final
 
   IntPoint m_mouseDownPos;  // In our view's coords.
   TimeTicks m_mouseDownTimestamp;
-  PlatformMouseEvent m_mouseDown;
+  WebMouseEvent m_mouseDown;
 
   LayoutPoint m_dragStartPos;
 
diff --git a/third_party/WebKit/Source/core/input/PointerEventManager.cpp b/third_party/WebKit/Source/core/input/PointerEventManager.cpp
index 3d22ce286adfef..ae2d1960c00134 100644
--- a/third_party/WebKit/Source/core/input/PointerEventManager.cpp
+++ b/third_party/WebKit/Source/core/input/PointerEventManager.cpp
@@ -180,12 +180,13 @@ EventTarget* PointerEventManager::getEffectiveTargetForPointerEvent(
 
 void PointerEventManager::sendMouseAndPointerBoundaryEvents(
     Node* enteredNode,
-    const PlatformMouseEvent& mouseEvent) {
+    const String& canvasRegionId,
+    const WebMouseEvent& mouseEvent) {
   // Mouse event type does not matter as this pointerevent will only be used
   // to create boundary pointer events and its type will be overridden in
   // |sendBoundaryEvents| function.
   PointerEvent* dummyPointerEvent = m_pointerEventFactory.create(
-      EventTypeNames::mousedown, mouseEvent, Vector<PlatformMouseEvent>(),
+      EventTypeNames::mousedown, mouseEvent, Vector<WebMouseEvent>(),
       m_frame->document()->domWindow());
 
   // TODO(crbug/545647): This state should reset with pointercancel too.
@@ -195,11 +196,11 @@ void PointerEventManager::sendMouseAndPointerBoundaryEvents(
   // behavior regarding preventMouseEvent state in that case.
   if (dummyPointerEvent->buttons() == 0 && dummyPointerEvent->isPrimary()) {
     m_preventMouseEventForPointerType[toPointerTypeIndex(
-        mouseEvent.pointerProperties().pointerType)] = false;
+        mouseEvent.pointerType)] = false;
   }
 
   processCaptureAndPositionOfPointerEvent(dummyPointerEvent, enteredNode,
-                                          mouseEvent, true);
+                                          canvasRegionId, mouseEvent, true);
 }
 
 void PointerEventManager::sendBoundaryEvents(EventTarget* exitedTarget,
@@ -439,9 +440,10 @@ WebInputEventResult PointerEventManager::sendTouchPointerEvent(
 
 WebInputEventResult PointerEventManager::sendMousePointerEvent(
     Node* target,
+    const String& canvasRegionId,
     const AtomicString& mouseEventType,
-    const PlatformMouseEvent& mouseEvent,
-    const Vector<PlatformMouseEvent>& coalescedEvents) {
+    const WebMouseEvent& mouseEvent,
+    const Vector<WebMouseEvent>& coalescedEvents) {
   PointerEvent* pointerEvent =
       m_pointerEventFactory.create(mouseEventType, mouseEvent, coalescedEvents,
                                    m_frame->document()->domWindow());
@@ -455,12 +457,12 @@ WebInputEventResult PointerEventManager::sendMousePointerEvent(
 
     if (pointerEvent->isPrimary()) {
       m_preventMouseEventForPointerType[toPointerTypeIndex(
-          mouseEvent.pointerProperties().pointerType)] = false;
+          mouseEvent.pointerType)] = false;
     }
   }
 
   EventTarget* pointerEventTarget = processCaptureAndPositionOfPointerEvent(
-      pointerEvent, target, mouseEvent, true);
+      pointerEvent, target, canvasRegionId, mouseEvent, true);
 
   EventTarget* effectiveTarget = getEffectiveTargetForPointerEvent(
       pointerEventTarget, pointerEvent->pointerId());
@@ -472,12 +474,12 @@ WebInputEventResult PointerEventManager::sendMousePointerEvent(
       pointerEvent->type() == EventTypeNames::pointerdown &&
       pointerEvent->isPrimary()) {
     m_preventMouseEventForPointerType[toPointerTypeIndex(
-        mouseEvent.pointerProperties().pointerType)] = true;
+        mouseEvent.pointerType)] = true;
   }
 
   if (pointerEvent->isPrimary() &&
       !m_preventMouseEventForPointerType[toPointerTypeIndex(
-          mouseEvent.pointerProperties().pointerType)]) {
+          mouseEvent.pointerType)]) {
     EventTarget* mouseTarget = effectiveTarget;
     // Event path could be null if pointer event is not dispatched and
     // that happens for example when pointer event feature is not enabled.
@@ -491,8 +493,9 @@ WebInputEventResult PointerEventManager::sendMousePointerEvent(
       }
     }
     result = EventHandlingUtil::mergeEventResult(
-        result, m_mouseEventManager->dispatchMouseEvent(
-                    mouseTarget, mouseEventType, mouseEvent, nullptr));
+        result,
+        m_mouseEventManager->dispatchMouseEvent(
+            mouseTarget, mouseEventType, mouseEvent, canvasRegionId, nullptr));
   }
 
   if (pointerEvent->type() == EventTypeNames::pointerup ||
@@ -503,7 +506,7 @@ WebInputEventResult PointerEventManager::sendMousePointerEvent(
 
     if (pointerEvent->isPrimary()) {
       m_preventMouseEventForPointerType[toPointerTypeIndex(
-          mouseEvent.pointerProperties().pointerType)] = false;
+          mouseEvent.pointerType)] = false;
     }
   }
 
@@ -534,7 +537,8 @@ bool PointerEventManager::getPointerCaptureState(
 EventTarget* PointerEventManager::processCaptureAndPositionOfPointerEvent(
     PointerEvent* pointerEvent,
     EventTarget* hitTestTarget,
-    const PlatformMouseEvent& mouseEvent,
+    const String& canvasRegionId,
+    const WebMouseEvent& mouseEvent,
     bool sendMouseEvent) {
   processPendingPointerCapture(pointerEvent);
 
@@ -547,7 +551,8 @@ EventTarget* PointerEventManager::processCaptureAndPositionOfPointerEvent(
   setNodeUnderPointer(pointerEvent, hitTestTarget);
   if (sendMouseEvent) {
     m_mouseEventManager->setNodeUnderMouse(
-        hitTestTarget ? hitTestTarget->toNode() : nullptr, mouseEvent);
+        hitTestTarget ? hitTestTarget->toNode() : nullptr, canvasRegionId,
+        mouseEvent);
   }
   return hitTestTarget;
 }
diff --git a/third_party/WebKit/Source/core/input/PointerEventManager.h b/third_party/WebKit/Source/core/input/PointerEventManager.h
index 8504f5c47b478e..0ba65f669b0e89 100644
--- a/third_party/WebKit/Source/core/input/PointerEventManager.h
+++ b/third_party/WebKit/Source/core/input/PointerEventManager.h
@@ -36,9 +36,10 @@ class CORE_EXPORT PointerEventManager
   // in this function.
   WebInputEventResult sendMousePointerEvent(
       Node* target,
+      const String& canvasRegionId,
       const AtomicString& type,
-      const PlatformMouseEvent&,
-      const Vector<PlatformMouseEvent>& coalescedEvents);
+      const WebMouseEvent&,
+      const Vector<WebMouseEvent>& coalescedEvents);
 
   WebInputEventResult handleTouchEvents(
       const WebTouchEvent&,
@@ -51,7 +52,8 @@ class CORE_EXPORT PointerEventManager
   // and their corresponding boundary events will be handled altogether by
   // sendMousePointerEvent function.
   void sendMouseAndPointerBoundaryEvents(Node* enteredNode,
-                                         const PlatformMouseEvent&);
+                                         const String& canvasRegionId,
+                                         const WebMouseEvent&);
 
   // Resets the internal state of this object.
   void clear();
@@ -168,7 +170,8 @@ class CORE_EXPORT PointerEventManager
   EventTarget* processCaptureAndPositionOfPointerEvent(
       PointerEvent*,
       EventTarget* hitTestTarget,
-      const PlatformMouseEvent& = PlatformMouseEvent(),
+      const String& canvasRegionId = String(),
+      const WebMouseEvent& = WebMouseEvent(),
       bool sendMouseEvent = false);
 
   void removeTargetFromPointerCapturingMapping(PointerCapturingMap&,
diff --git a/third_party/WebKit/Source/core/input/ScrollManager.cpp b/third_party/WebKit/Source/core/input/ScrollManager.cpp
index 0a5c306b0383dd..12de4c6bf407d4 100644
--- a/third_party/WebKit/Source/core/input/ScrollManager.cpp
+++ b/third_party/WebKit/Source/core/input/ScrollManager.cpp
@@ -506,11 +506,12 @@ bool ScrollManager::inResizeMode() const {
   return m_resizeScrollableArea && m_resizeScrollableArea->inResizeMode();
 }
 
-void ScrollManager::resize(const PlatformMouseEvent& evt) {
-  if (evt.type() == PlatformEvent::MouseMoved) {
+void ScrollManager::resize(const WebMouseEvent& evt) {
+  if (evt.type() == WebInputEvent::MouseMove) {
     if (!m_frame->eventHandler().mousePressed())
       return;
-    m_resizeScrollableArea->resize(evt.position(), m_offsetFromResizeCorner);
+    m_resizeScrollableArea->resize(flooredIntPoint(evt.positionInRootFrame()),
+                                   m_offsetFromResizeCorner);
   }
 }
 
diff --git a/third_party/WebKit/Source/core/input/ScrollManager.h b/third_party/WebKit/Source/core/input/ScrollManager.h
index a5f69d79d4ac6d..b87e24419aa247 100644
--- a/third_party/WebKit/Source/core/input/ScrollManager.h
+++ b/third_party/WebKit/Source/core/input/ScrollManager.h
@@ -86,7 +86,7 @@ class CORE_EXPORT ScrollManager
 
   // These functions are related to |m_resizeScrollableArea|.
   bool inResizeMode() const;
-  void resize(const PlatformMouseEvent&);
+  void resize(const WebMouseEvent&);
   // Clears |m_resizeScrollableArea|. if |shouldNotBeNull| is true this
   // function DCHECKs to make sure that variable is indeed not null.
   void clearResizeScrollableArea(bool shouldNotBeNull);
diff --git a/third_party/WebKit/Source/core/inspector/InspectorDOMAgent.cpp b/third_party/WebKit/Source/core/inspector/InspectorDOMAgent.cpp
index bbb87a7d505512..8cfe3a1afa7d2b 100644
--- a/third_party/WebKit/Source/core/inspector/InspectorDOMAgent.cpp
+++ b/third_party/WebKit/Source/core/inspector/InspectorDOMAgent.cpp
@@ -75,7 +75,6 @@
 #include "core/page/Page.h"
 #include "core/xml/DocumentXPathEvaluator.h"
 #include "core/xml/XPathResult.h"
-#include "platform/PlatformMouseEvent.h"
 #include "wtf/ListHashSet.h"
 #include "wtf/PtrUtil.h"
 #include "wtf/text/CString.h"
diff --git a/third_party/WebKit/Source/core/layout/HitTestResult.cpp b/third_party/WebKit/Source/core/layout/HitTestResult.cpp
index 76f4cd952ed4d7..b1b70ee934d3e4 100644
--- a/third_party/WebKit/Source/core/layout/HitTestResult.cpp
+++ b/third_party/WebKit/Source/core/layout/HitTestResult.cpp
@@ -92,7 +92,8 @@ HitTestResult::HitTestResult(const HitTestResult& other)
       m_localPoint(other.localPoint()),
       m_innerURLElement(other.URLElement()),
       m_scrollbar(other.scrollbar()),
-      m_isOverWidget(other.isOverWidget()) {
+      m_isOverWidget(other.isOverWidget()),
+      m_canvasRegionId(other.canvasRegionId()) {
   // Only copy the NodeSet in case of list hit test.
   m_listBasedTestResult = other.m_listBasedTestResult
                               ? new NodeSet(*other.m_listBasedTestResult)
@@ -135,6 +136,7 @@ void HitTestResult::populateFromCachedResult(const HitTestResult& other) {
   m_scrollbar = other.scrollbar();
   m_isOverWidget = other.isOverWidget();
   m_cacheable = other.m_cacheable;
+  m_canvasRegionId = other.canvasRegionId();
 
   // Only copy the NodeSet in case of list hit test.
   m_listBasedTestResult = other.m_listBasedTestResult
@@ -438,6 +440,7 @@ void HitTestResult::append(const HitTestResult& other) {
     m_pointInInnerNodeFrame = other.m_pointInInnerNodeFrame;
     m_innerURLElement = other.URLElement();
     m_isOverWidget = other.isOverWidget();
+    m_canvasRegionId = other.canvasRegionId();
   }
 
   if (other.m_listBasedTestResult) {
diff --git a/third_party/WebKit/Source/core/layout/HitTestResult.h b/third_party/WebKit/Source/core/layout/HitTestResult.h
index 18225cff8b1ee1..ff5c464228f02e 100644
--- a/third_party/WebKit/Source/core/layout/HitTestResult.h
+++ b/third_party/WebKit/Source/core/layout/HitTestResult.h
@@ -154,6 +154,9 @@ class CORE_EXPORT HitTestResult {
   bool isLiveLink() const;
   bool isContentEditable() const;
 
+  const String& canvasRegionId() const { return m_canvasRegionId; }
+  void setCanvasRegionId(const String& id) { m_canvasRegionId = id; }
+
   bool isOverLink() const;
 
   bool isCacheable() const { return m_cacheable; }
@@ -208,6 +211,7 @@ class CORE_EXPORT HitTestResult {
                         // border/padding area of a LayoutPart for example).
 
   mutable Member<NodeSet> m_listBasedTestResult;
+  String m_canvasRegionId;
 };
 
 }  // namespace blink
diff --git a/third_party/WebKit/Source/core/layout/LayoutScrollbarTheme.h b/third_party/WebKit/Source/core/layout/LayoutScrollbarTheme.h
index c9b96ebebe0203..de89c064fee666 100644
--- a/third_party/WebKit/Source/core/layout/LayoutScrollbarTheme.h
+++ b/third_party/WebKit/Source/core/layout/LayoutScrollbarTheme.h
@@ -30,7 +30,7 @@
 
 namespace blink {
 
-class PlatformMouseEvent;
+class WebMouseEvent;
 
 class LayoutScrollbarTheme final : public ScrollbarTheme {
  public:
@@ -49,11 +49,11 @@ class LayoutScrollbarTheme final : public ScrollbarTheme {
                          const IntRect& cornerRect) override;
 
   bool shouldCenterOnThumb(const ScrollbarThemeClient& scrollbar,
-                           const PlatformMouseEvent& event) override {
+                           const WebMouseEvent& event) override {
     return ScrollbarTheme::theme().shouldCenterOnThumb(scrollbar, event);
   }
   bool shouldSnapBackToDragOrigin(const ScrollbarThemeClient& scrollbar,
-                                  const PlatformMouseEvent& event) override {
+                                  const WebMouseEvent& event) override {
     return ScrollbarTheme::theme().shouldSnapBackToDragOrigin(scrollbar, event);
   }
 
diff --git a/third_party/WebKit/Source/core/page/AutoscrollController.cpp b/third_party/WebKit/Source/core/page/AutoscrollController.cpp
index 748b48dae496bd..86c673226055e7 100644
--- a/third_party/WebKit/Source/core/page/AutoscrollController.cpp
+++ b/third_party/WebKit/Source/core/page/AutoscrollController.cpp
@@ -203,14 +203,13 @@ void AutoscrollController::updateDragAndDrop(Node* dropTargetNode,
 
 void AutoscrollController::handleMouseReleaseForMiddleClickAutoscroll(
     LocalFrame* frame,
-    const PlatformMouseEvent& mouseEvent) {
+    const WebMouseEvent& mouseEvent) {
   DCHECK(RuntimeEnabledFeatures::middleClickAutoscrollEnabled());
   if (!frame->isMainFrame())
     return;
   switch (m_autoscrollType) {
     case AutoscrollForMiddleClick:
-      if (mouseEvent.pointerProperties().button ==
-          WebPointerProperties::Button::Middle)
+      if (mouseEvent.button == WebPointerProperties::Button::Middle)
         m_autoscrollType = AutoscrollForMiddleClickCanStop;
       break;
     case AutoscrollForMiddleClickCanStop:
diff --git a/third_party/WebKit/Source/core/page/AutoscrollController.h b/third_party/WebKit/Source/core/page/AutoscrollController.h
index aab9602b556b8e..5ab08a0267b859 100644
--- a/third_party/WebKit/Source/core/page/AutoscrollController.h
+++ b/third_party/WebKit/Source/core/page/AutoscrollController.h
@@ -38,9 +38,9 @@ class LocalFrame;
 class FrameView;
 class Node;
 class Page;
-class PlatformMouseEvent;
 class LayoutBox;
 class LayoutObject;
+class WebMouseEvent;
 
 enum AutoscrollType {
   NoAutoscroll,
@@ -72,7 +72,7 @@ class CORE_EXPORT AutoscrollController final
                          const IntPoint& eventPosition,
                          TimeTicks eventTime);
   void handleMouseReleaseForMiddleClickAutoscroll(LocalFrame*,
-                                                  const PlatformMouseEvent&);
+                                                  const WebMouseEvent&);
   void startMiddleClickAutoscroll(LayoutBox*, const IntPoint&);
 
  private:
diff --git a/third_party/WebKit/Source/core/page/ContextMenuControllerTest.cpp b/third_party/WebKit/Source/core/page/ContextMenuControllerTest.cpp
index 94435af81d3443..ae1100cbf14db0 100644
--- a/third_party/WebKit/Source/core/page/ContextMenuControllerTest.cpp
+++ b/third_party/WebKit/Source/core/page/ContextMenuControllerTest.cpp
@@ -76,11 +76,15 @@ TEST_F(ContextMenuControllerTest, TestCustomMenu) {
       "</menu>"
       "</button>");
 
+  MouseEventInit mouseInitializer;
+  mouseInitializer.setView(document().domWindow());
+  mouseInitializer.setScreenX(50);
+  mouseInitializer.setScreenY(50);
+  mouseInitializer.setButton(1);
+
   // Create right button click event and pass it to context menu controller.
-  Event* event = MouseEvent::create(
-      EventTypeNames::click, false, false, document().domWindow(), 50, 50, 0, 0,
-      0, 0, 0, PlatformEvent::NoModifiers, 1, 0, nullptr, TimeTicks(),
-      PlatformMouseEvent::RealOrIndistinguishable, String(), nullptr);
+  Event* event =
+      MouseEvent::create(nullptr, EventTypeNames::click, mouseInitializer);
   document().getElementById("button_id")->focus();
   event->setTarget(document().getElementById("button_id"));
   document().page()->contextMenuController().handleContextMenuEvent(event);
diff --git a/third_party/WebKit/Source/core/page/DragController.cpp b/third_party/WebKit/Source/core/page/DragController.cpp
index c9eef0f9997b00..07385275214487 100644
--- a/third_party/WebKit/Source/core/page/DragController.cpp
+++ b/third_party/WebKit/Source/core/page/DragController.cpp
@@ -118,12 +118,19 @@ static bool dragTypeIsValid(DragSourceAction action) {
 }
 #endif  // DCHECK_IS_ON()
 
-static PlatformMouseEvent createMouseEvent(DragData* dragData) {
-  return PlatformMouseEvent(
-      dragData->clientPosition(), dragData->globalPosition(),
-      WebPointerProperties::Button::Left, PlatformEvent::MouseMoved, 0,
+static WebMouseEvent createMouseEvent(DragData* dragData) {
+  WebMouseEvent result(
+      WebInputEvent::MouseMove, WebFloatPoint(dragData->clientPosition().x(),
+                                              dragData->clientPosition().y()),
+      WebFloatPoint(dragData->globalPosition().x(),
+                    dragData->globalPosition().y()),
+      WebPointerProperties::Button::Left, 0,
       static_cast<PlatformEvent::Modifiers>(dragData->modifiers()),
-      PlatformMouseEvent::RealOrIndistinguishable, TimeTicks::Now());
+      TimeTicks::Now().InSeconds());
+  // TODO(dtapuska): Really we should chnage DragData to store the viewport
+  // coordinates and scale.
+  result.setFrameScale(1);
+  return result;
 }
 
 static DataTransfer* createDraggingDataTransfer(DataTransferAccessPolicy policy,
@@ -719,7 +726,7 @@ bool DragController::tryDHTMLDrag(DragData* dragData,
   DragOperation srcOpMask = dragData->draggingSourceOperationMask();
   dataTransfer->setSourceOperation(srcOpMask);
 
-  PlatformMouseEvent event = createMouseEvent(dragData);
+  WebMouseEvent event = createMouseEvent(dragData);
   if (localRoot.eventHandler().updateDragAndDrop(event, dataTransfer) ==
       WebInputEventResult::NotHandled) {
     dataTransfer->setAccessPolicy(
@@ -1050,7 +1057,7 @@ static std::unique_ptr<DragImage> dragImageForLink(
 
 bool DragController::startDrag(LocalFrame* src,
                                const DragState& state,
-                               const PlatformMouseEvent& dragEvent,
+                               const WebMouseEvent& dragEvent,
                                const IntPoint& dragOrigin) {
 #if DCHECK_IS_ON()
   DCHECK(dragTypeIsValid(state.m_dragType));
@@ -1072,8 +1079,8 @@ bool DragController::startDrag(LocalFrame* src,
   const KURL& linkURL = hitTestResult.absoluteLinkURL();
   const KURL& imageURL = hitTestResult.absoluteImageURL();
 
-  IntPoint mouseDraggedPoint =
-      src->view()->rootFrameToContents(dragEvent.position());
+  IntPoint mouseDraggedPoint = src->view()->rootFrameToContents(
+      flooredIntPoint(dragEvent.positionInRootFrame()));
 
   IntPoint dragLocation;
   IntPoint dragOffset;
diff --git a/third_party/WebKit/Source/core/page/DragController.h b/third_party/WebKit/Source/core/page/DragController.h
index 3d28be6cf3b6d2..763f6576dcffc8 100644
--- a/third_party/WebKit/Source/core/page/DragController.h
+++ b/third_party/WebKit/Source/core/page/DragController.h
@@ -47,7 +47,7 @@ class FrameSelection;
 class HTMLInputElement;
 class Node;
 class Page;
-class PlatformMouseEvent;
+class WebMouseEvent;
 
 class CORE_EXPORT DragController final
     : public GarbageCollected<DragController> {
@@ -76,7 +76,7 @@ class CORE_EXPORT DragController final
                                 const IntPoint& dragOrigin);
   bool startDrag(LocalFrame* src,
                  const DragState&,
-                 const PlatformMouseEvent& dragEvent,
+                 const WebMouseEvent& dragEvent,
                  const IntPoint& dragOrigin);
 
   DECLARE_TRACE();
diff --git a/third_party/WebKit/Source/core/page/EventWithHitTestResults.h b/third_party/WebKit/Source/core/page/EventWithHitTestResults.h
index 9d0bdb7b5c4513..b8292558340782 100644
--- a/third_party/WebKit/Source/core/page/EventWithHitTestResults.h
+++ b/third_party/WebKit/Source/core/page/EventWithHitTestResults.h
@@ -23,8 +23,8 @@
 
 #include "core/layout/HitTestResult.h"
 #include "platform/PlatformEvent.h"
-#include "platform/PlatformMouseEvent.h"
 #include "public/platform/WebGestureEvent.h"
+#include "public/platform/WebMouseEvent.h"
 
 namespace blink {
 
@@ -46,14 +46,16 @@ class EventWithHitTestResults {
   bool isOverLink() const { return m_hitTestResult.isOverLink(); }
   bool isOverWidget() const { return m_hitTestResult.isOverWidget(); }
   Node* innerNode() const { return m_hitTestResult.innerNode(); }
+  const String& canvasRegionId() const {
+    return m_hitTestResult.canvasRegionId();
+  }
 
  private:
   EventType m_event;
   HitTestResult m_hitTestResult;
 };
 
-using MouseEventWithHitTestResults =
-    EventWithHitTestResults<PlatformMouseEvent>;
+using MouseEventWithHitTestResults = EventWithHitTestResults<WebMouseEvent>;
 
 using GestureEventWithHitTestResults = EventWithHitTestResults<WebGestureEvent>;
 
diff --git a/third_party/WebKit/Source/core/page/PointerLockController.cpp b/third_party/WebKit/Source/core/page/PointerLockController.cpp
index 720e004db740ab..97b298bd9d5cd7 100644
--- a/third_party/WebKit/Source/core/page/PointerLockController.cpp
+++ b/third_party/WebKit/Source/core/page/PointerLockController.cpp
@@ -31,7 +31,7 @@
 #include "core/inspector/ConsoleMessage.h"
 #include "core/page/ChromeClient.h"
 #include "core/page/Page.h"
-#include "platform/PlatformMouseEvent.h"
+#include "public/platform/WebMouseEvent.h"
 
 namespace blink {
 
@@ -132,17 +132,18 @@ void PointerLockController::didLosePointerLock() {
 }
 
 void PointerLockController::dispatchLockedMouseEvent(
-    const PlatformMouseEvent& event,
+    const WebMouseEvent& event,
     const AtomicString& eventType) {
   if (!m_element || !m_element->document().frame())
     return;
 
-  m_element->dispatchMouseEvent(event, eventType, event.clickCount());
+  m_element->dispatchMouseEvent(event, eventType, event.clickCount);
 
   // Create click events
-  if (eventType == EventTypeNames::mouseup)
+  if (eventType == EventTypeNames::mouseup) {
     m_element->dispatchMouseEvent(event, EventTypeNames::click,
-                                  event.clickCount());
+                                  event.clickCount);
+  }
 }
 
 void PointerLockController::clearElement() {
diff --git a/third_party/WebKit/Source/core/page/PointerLockController.h b/third_party/WebKit/Source/core/page/PointerLockController.h
index cea1abb727ba42..d4caa2fa4d8c6c 100644
--- a/third_party/WebKit/Source/core/page/PointerLockController.h
+++ b/third_party/WebKit/Source/core/page/PointerLockController.h
@@ -36,7 +36,7 @@ namespace blink {
 class Element;
 class Document;
 class Page;
-class PlatformMouseEvent;
+class WebMouseEvent;
 
 class CORE_EXPORT PointerLockController final
     : public GarbageCollected<PointerLockController> {
@@ -55,7 +55,7 @@ class CORE_EXPORT PointerLockController final
   void didAcquirePointerLock();
   void didNotAcquirePointerLock();
   void didLosePointerLock();
-  void dispatchLockedMouseEvent(const PlatformMouseEvent&,
+  void dispatchLockedMouseEvent(const WebMouseEvent&,
                                 const AtomicString& eventType);
 
   DECLARE_TRACE();
diff --git a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
index 894d81f85ace40..4b9c6d9c2fd6f9 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
@@ -78,7 +78,6 @@
 #include "core/page/scrolling/ScrollingCoordinator.h"
 #include "core/page/scrolling/TopDocumentRootScrollerController.h"
 #include "core/paint/PaintLayerFragment.h"
-#include "platform/PlatformMouseEvent.h"
 #include "platform/graphics/CompositorMutableProperties.h"
 #include "platform/graphics/GraphicsLayer.h"
 #include "platform/graphics/paint/DrawingRecorder.h"
diff --git a/third_party/WebKit/Source/core/svg/SVGAElement.cpp b/third_party/WebKit/Source/core/svg/SVGAElement.cpp
index 6dec847d065afa..a3283c6c2cd069 100644
--- a/third_party/WebKit/Source/core/svg/SVGAElement.cpp
+++ b/third_party/WebKit/Source/core/svg/SVGAElement.cpp
@@ -44,7 +44,6 @@
 #include "core/page/ChromeClient.h"
 #include "core/page/Page.h"
 #include "core/svg/animation/SVGSMILElement.h"
-#include "platform/PlatformMouseEvent.h"
 #include "platform/network/ResourceRequest.h"
 
 namespace blink {
diff --git a/third_party/WebKit/Source/platform/BUILD.gn b/third_party/WebKit/Source/platform/BUILD.gn
index c100adca21895c..0c685232ad70ed 100644
--- a/third_party/WebKit/Source/platform/BUILD.gn
+++ b/third_party/WebKit/Source/platform/BUILD.gn
@@ -304,7 +304,6 @@ component("platform") {
     "PlatformEvent.h",
     "PlatformInstrumentation.cpp",
     "PlatformInstrumentation.h",
-    "PlatformMouseEvent.h",
     "PlatformResourceLoader.cpp",
     "PlatformResourceLoader.h",
     "PluginScriptForbiddenScope.cpp",
diff --git a/third_party/WebKit/Source/platform/PlatformEvent.h b/third_party/WebKit/Source/platform/PlatformEvent.h
index d8c09cb4a7e98f..21ab74ce7f883f 100644
--- a/third_party/WebKit/Source/platform/PlatformEvent.h
+++ b/third_party/WebKit/Source/platform/PlatformEvent.h
@@ -36,12 +36,6 @@ class PlatformEvent {
  public:
   enum EventType {
     NoType = 0,
-
-    // PlatformMouseEvent
-    MouseMoved,
-    MousePressed,
-    MouseReleased,
-    MouseScroll,
   };
 
   // These values are direct mappings of the values in WebInputEvent so the
diff --git a/third_party/WebKit/Source/platform/PlatformMouseEvent.h b/third_party/WebKit/Source/platform/PlatformMouseEvent.h
deleted file mode 100644
index f8234d74549a32..00000000000000
--- a/third_party/WebKit/Source/platform/PlatformMouseEvent.h
+++ /dev/null
@@ -1,150 +0,0 @@
-/*
- * Copyright (C) 2004, 2005, 2006, 2009 Apple Inc. All rights reserved.
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- * 1. Redistributions of source code must retain the above copyright
- *    notice, this list of conditions and the following disclaimer.
- * 2. Redistributions in binary form must reproduce the above copyright
- *    notice, this list of conditions and the following disclaimer in the
- *    documentation and/or other materials provided with the distribution.
- *
- * THIS SOFTWARE IS PROVIDED BY APPLE COMPUTER, INC. ``AS IS'' AND ANY
- * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
- * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
- * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE COMPUTER, INC. OR
- * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
- * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
- * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
- * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
- * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
- * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
- * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
- */
-
-#ifndef PlatformMouseEvent_h
-#define PlatformMouseEvent_h
-
-#include "platform/PlatformEvent.h"
-#include "platform/geometry/FloatPoint.h"
-#include "platform/geometry/IntPoint.h"
-#include "public/platform/WebGestureEvent.h"
-#include "public/platform/WebPointerProperties.h"
-#include "wtf/text/WTFString.h"
-
-namespace blink {
-
-class PlatformMouseEvent : public PlatformEvent {
- public:
-  enum SyntheticEventType {
-    // Real mouse input events or synthetic events that behave just like real
-    // events
-    RealOrIndistinguishable,
-    // Synthetic mouse events derived from touch input
-    FromTouch,
-    // Synthetic mouse events generated without a position, for example those
-    // generated from keyboard input.
-    Positionless,
-  };
-
-  PlatformMouseEvent() : PlatformMouseEvent(PlatformEvent::MouseMoved) {}
-
-  explicit PlatformMouseEvent(EventType type)
-      : PlatformEvent(type),
-        m_clickCount(0),
-        m_synthesized(RealOrIndistinguishable) {}
-
-  PlatformMouseEvent(const IntPoint& position,
-                     const IntPoint& globalPosition,
-                     WebPointerProperties::Button button,
-                     EventType type,
-                     int clickCount,
-                     Modifiers modifiers,
-                     TimeTicks timestamp)
-      : PlatformEvent(type, modifiers, timestamp),
-        m_position(position),
-        m_globalPosition(globalPosition),
-        m_clickCount(clickCount),
-        m_synthesized(RealOrIndistinguishable) {
-    m_pointerProperties.button = button;
-  }
-
-  PlatformMouseEvent(const IntPoint& position,
-                     const IntPoint& globalPosition,
-                     WebPointerProperties::Button button,
-                     EventType type,
-                     int clickCount,
-                     Modifiers modifiers,
-                     SyntheticEventType synthesized,
-                     TimeTicks timestamp,
-                     WebPointerProperties::PointerType pointerType =
-                         WebPointerProperties::PointerType::Unknown)
-      : PlatformEvent(type, modifiers, timestamp),
-        m_position(position),
-        m_globalPosition(globalPosition),
-        m_clickCount(clickCount),
-        m_synthesized(synthesized) {
-    m_pointerProperties.pointerType = pointerType;
-    m_pointerProperties.button = button;
-  }
-
-#if INSIDE_BLINK
-  PlatformMouseEvent(const WebGestureEvent& gestureEvent,
-                     WebPointerProperties::Button button,
-                     EventType type,
-                     int clickCount,
-                     Modifiers modifiers,
-                     SyntheticEventType synthesized,
-                     TimeTicks timestamp,
-                     WebPointerProperties::PointerType pointerType =
-                         WebPointerProperties::PointerType::Unknown)
-      : PlatformMouseEvent(flooredIntPoint(gestureEvent.positionInRootFrame()),
-                           IntPoint(gestureEvent.globalX, gestureEvent.globalY),
-                           button,
-                           type,
-                           clickCount,
-                           modifiers,
-                           synthesized,
-                           timestamp,
-                           pointerType) {}
-#endif
-
-  const WebPointerProperties& pointerProperties() const {
-    return m_pointerProperties;
-  }
-  const IntPoint& position() const { return m_position; }
-  const IntPoint& globalPosition() const { return m_globalPosition; }
-  const IntPoint& movementDelta() const { return m_movementDelta; }
-
-  int clickCount() const { return m_clickCount; }
-  bool fromTouch() const { return m_synthesized == FromTouch; }
-  SyntheticEventType getSyntheticEventType() const { return m_synthesized; }
-
-  const String& region() const { return m_region; }
-  void setRegion(const String& region) { m_region = region; }
-
- protected:
-  WebPointerProperties m_pointerProperties;
-
-  // In local root frame coordinates. (Except possibly if the Widget under
-  // the mouse is a popup, see FIXME in PlatformMouseEventBuilder).
-  IntPoint m_position;
-
-  // In screen coordinates.
-  IntPoint m_globalPosition;
-
-  IntPoint m_movementDelta;
-  int m_clickCount;
-  SyntheticEventType m_synthesized;
-
-  // For canvas hit region.
-  // TODO(zino): This might make more sense to put in HitTestResults or
-  // some other part of MouseEventWithHitTestResults, but for now it's
-  // most convenient to stash it here. Please see: http://crbug.com/592947.
-  String m_region;
-};
-
-}  // namespace blink
-
-#endif  // PlatformMouseEvent_h
diff --git a/third_party/WebKit/Source/platform/WebMouseEvent.cpp b/third_party/WebKit/Source/platform/WebMouseEvent.cpp
index 4e6e9575f02fe7..8e297fa165b3b6 100644
--- a/third_party/WebKit/Source/platform/WebMouseEvent.cpp
+++ b/third_party/WebKit/Source/platform/WebMouseEvent.cpp
@@ -4,8 +4,28 @@
 
 #include "public/platform/WebMouseEvent.h"
 
+#include "public/platform/WebGestureEvent.h"
+
 namespace blink {
 
+WebMouseEvent::WebMouseEvent(WebInputEvent::Type type,
+                             const WebGestureEvent& gestureEvent,
+                             Button buttonParam,
+                             int clickCountParam,
+                             int modifiers,
+                             double timeStampSeconds)
+    : WebInputEvent(sizeof(WebMouseEvent), type, modifiers, timeStampSeconds),
+      WebPointerProperties(buttonParam,
+                           WebPointerProperties::PointerType::Mouse),
+      x(gestureEvent.x),
+      y(gestureEvent.y),
+      globalX(gestureEvent.globalX),
+      globalY(gestureEvent.globalY),
+      clickCount(clickCountParam) {
+  setFrameScale(gestureEvent.frameScale());
+  setFrameTranslate(gestureEvent.frameTranslate());
+}
+
 WebFloatPoint WebMouseEvent::movementInRootFrame() const {
   return WebFloatPoint((movementX / m_frameScale), (movementY / m_frameScale));
 }
@@ -15,6 +35,12 @@ WebFloatPoint WebMouseEvent::positionInRootFrame() const {
                        (y / m_frameScale) + m_frameTranslate.y);
 }
 
+WebMouseEvent WebMouseEvent::flattenTransform() const {
+  WebMouseEvent result = *this;
+  result.flattenTransformSelf();
+  return result;
+}
+
 void WebMouseEvent::flattenTransformSelf() {
   x = (x / m_frameScale) + m_frameTranslate.x;
   y = (y / m_frameScale) + m_frameTranslate.y;
diff --git a/third_party/WebKit/Source/platform/scroll/Scrollbar.cpp b/third_party/WebKit/Source/platform/scroll/Scrollbar.cpp
index 442518dddee697..cd3b8accdf87d8 100644
--- a/third_party/WebKit/Source/platform/scroll/Scrollbar.cpp
+++ b/third_party/WebKit/Source/platform/scroll/Scrollbar.cpp
@@ -27,13 +27,13 @@
 
 #include <algorithm>
 #include "platform/HostWindow.h"
-#include "platform/PlatformMouseEvent.h"
 #include "platform/geometry/FloatRect.h"
 #include "platform/graphics/paint/CullRect.h"
 #include "platform/scroll/ScrollAnimatorBase.h"
 #include "platform/scroll/ScrollableArea.h"
 #include "platform/scroll/ScrollbarTheme.h"
 #include "public/platform/WebGestureEvent.h"
+#include "public/platform/WebMouseEvent.h"
 
 namespace blink {
 
@@ -418,7 +418,8 @@ bool Scrollbar::gestureEvent(const WebGestureEvent& evt,
   }
 }
 
-void Scrollbar::mouseMoved(const PlatformMouseEvent& evt) {
+void Scrollbar::mouseMoved(const WebMouseEvent& evt) {
+  IntPoint position = flooredIntPoint(evt.positionInRootFrame());
   if (m_pressedPart == ThumbPart) {
     if (theme().shouldSnapBackToDragOrigin(*this, evt)) {
       if (m_scrollableArea) {
@@ -429,19 +430,20 @@ void Scrollbar::mouseMoved(const PlatformMouseEvent& evt) {
       }
     } else {
       moveThumb(m_orientation == HorizontalScrollbar
-                    ? convertFromRootFrame(evt.position()).x()
-                    : convertFromRootFrame(evt.position()).y(),
+                    ? convertFromRootFrame(position).x()
+                    : convertFromRootFrame(position).y(),
                 theme().shouldDragDocumentInsteadOfThumb(*this, evt));
     }
     return;
   }
 
-  if (m_pressedPart != NoPart)
+  if (m_pressedPart != NoPart) {
     m_pressedPos = orientation() == HorizontalScrollbar
-                       ? convertFromRootFrame(evt.position()).x()
-                       : convertFromRootFrame(evt.position()).y();
+                       ? convertFromRootFrame(position).x()
+                       : convertFromRootFrame(position).y();
+  }
 
-  ScrollbarPart part = theme().hitTest(*this, evt.position());
+  ScrollbarPart part = theme().hitTest(*this, position);
   if (part != m_hoveredPart) {
     if (m_pressedPart != NoPart) {
       if (part == m_pressedPart) {
@@ -472,7 +474,7 @@ void Scrollbar::mouseExited() {
   setHoveredPart(NoPart);
 }
 
-void Scrollbar::mouseUp(const PlatformMouseEvent& mouseEvent) {
+void Scrollbar::mouseUp(const WebMouseEvent& mouseEvent) {
   bool isCaptured = m_pressedPart == ThumbPart;
   setPressedPart(NoPart);
   m_pressedPos = 0;
@@ -483,7 +485,8 @@ void Scrollbar::mouseUp(const PlatformMouseEvent& mouseEvent) {
     if (isCaptured)
       m_scrollableArea->mouseReleasedScrollbar();
 
-    ScrollbarPart part = theme().hitTest(*this, mouseEvent.position());
+    ScrollbarPart part = theme().hitTest(
+        *this, flooredIntPoint(mouseEvent.positionInRootFrame()));
     if (part == NoPart) {
       setHoveredPart(NoPart);
       m_scrollableArea->mouseExitedScrollbar(*this);
@@ -491,15 +494,16 @@ void Scrollbar::mouseUp(const PlatformMouseEvent& mouseEvent) {
   }
 }
 
-void Scrollbar::mouseDown(const PlatformMouseEvent& evt) {
+void Scrollbar::mouseDown(const WebMouseEvent& evt) {
   // Early exit for right click
-  if (evt.pointerProperties().button == WebPointerProperties::Button::Right)
+  if (evt.button == WebPointerProperties::Button::Right)
     return;
 
-  setPressedPart(theme().hitTest(*this, evt.position()));
+  IntPoint position = flooredIntPoint(evt.positionInRootFrame());
+  setPressedPart(theme().hitTest(*this, position));
   int pressedPos = orientation() == HorizontalScrollbar
-                       ? convertFromRootFrame(evt.position()).x()
-                       : convertFromRootFrame(evt.position()).y();
+                       ? convertFromRootFrame(position).x()
+                       : convertFromRootFrame(position).y();
 
   if ((m_pressedPart == BackTrackPart || m_pressedPart == ForwardTrackPart) &&
       theme().shouldCenterOnThumb(*this, evt)) {
diff --git a/third_party/WebKit/Source/platform/scroll/Scrollbar.h b/third_party/WebKit/Source/platform/scroll/Scrollbar.h
index 6af3ef15384849..914c9aa3f535b4 100644
--- a/third_party/WebKit/Source/platform/scroll/Scrollbar.h
+++ b/third_party/WebKit/Source/platform/scroll/Scrollbar.h
@@ -39,10 +39,10 @@ namespace blink {
 class GraphicsContext;
 class HostWindow;
 class IntRect;
-class PlatformMouseEvent;
 class ScrollableArea;
 class ScrollbarTheme;
 class WebGestureEvent;
+class WebMouseEvent;
 
 class PLATFORM_EXPORT Scrollbar : public Widget,
                                   public ScrollbarThemeClient,
@@ -145,14 +145,14 @@ class PLATFORM_EXPORT Scrollbar : public Widget,
   // They will not get called when the mouse went down in a scrollbar, since it
   // is assumed the scrollbar will start
   // grabbing all events in that case anyway.
-  void mouseMoved(const PlatformMouseEvent&);
+  void mouseMoved(const WebMouseEvent&);
   void mouseEntered();
   void mouseExited();
 
   // Used by some platform scrollbars to know when they've been released from
   // capture.
-  void mouseUp(const PlatformMouseEvent&);
-  void mouseDown(const PlatformMouseEvent&);
+  void mouseUp(const WebMouseEvent&);
+  void mouseDown(const WebMouseEvent&);
 
   ScrollbarTheme& theme() const { return m_theme; }
 
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollbarTheme.cpp b/third_party/WebKit/Source/platform/scroll/ScrollbarTheme.cpp
index 00b2e022398ea7..91c715962d6a17 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollbarTheme.cpp
+++ b/third_party/WebKit/Source/platform/scroll/ScrollbarTheme.cpp
@@ -25,7 +25,6 @@
 
 #include "platform/scroll/ScrollbarTheme.h"
 
-#include "platform/PlatformMouseEvent.h"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/graphics/Color.h"
 #include "platform/graphics/GraphicsContext.h"
@@ -39,6 +38,7 @@
 #include "platform/scroll/ScrollbarThemeMock.h"
 #include "platform/scroll/ScrollbarThemeOverlayMock.h"
 #include "public/platform/Platform.h"
+#include "public/platform/WebMouseEvent.h"
 #include "public/platform/WebPoint.h"
 #include "public/platform/WebRect.h"
 #include "public/platform/WebScrollbarBehavior.h"
@@ -219,9 +219,10 @@ void ScrollbarTheme::paintScrollCorner(
 }
 
 bool ScrollbarTheme::shouldCenterOnThumb(const ScrollbarThemeClient& scrollbar,
-                                         const PlatformMouseEvent& evt) {
+                                         const WebMouseEvent& evt) {
   return Platform::current()->scrollbarBehavior()->shouldCenterOnThumb(
-      evt.pointerProperties().button, evt.shiftKey(), evt.altKey());
+      evt.button, evt.modifiers() & WebInputEvent::ShiftKey,
+      evt.modifiers() & WebInputEvent::AltKey);
 }
 
 void ScrollbarTheme::paintTickmarks(GraphicsContext& context,
@@ -270,8 +271,9 @@ void ScrollbarTheme::paintTickmarks(GraphicsContext& context,
 
 bool ScrollbarTheme::shouldSnapBackToDragOrigin(
     const ScrollbarThemeClient& scrollbar,
-    const PlatformMouseEvent& evt) {
-  IntPoint mousePosition = scrollbar.convertFromRootFrame(evt.position());
+    const WebMouseEvent& evt) {
+  IntPoint mousePosition = scrollbar.convertFromRootFrame(
+      flooredIntPoint(evt.positionInRootFrame()));
   mousePosition.move(scrollbar.x(), scrollbar.y());
   return Platform::current()->scrollbarBehavior()->shouldSnapBackToDragOrigin(
       mousePosition, trackRect(scrollbar),
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollbarTheme.h b/third_party/WebKit/Source/platform/scroll/ScrollbarTheme.h
index 948af5645e1bb5..a7a5f702f1c91f 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollbarTheme.h
+++ b/third_party/WebKit/Source/platform/scroll/ScrollbarTheme.h
@@ -37,7 +37,7 @@ namespace blink {
 
 class CullRect;
 class GraphicsContext;
-class PlatformMouseEvent;
+class WebMouseEvent;
 
 class PLATFORM_EXPORT ScrollbarTheme {
   WTF_MAKE_NONCOPYABLE(ScrollbarTheme);
@@ -106,11 +106,11 @@ class PLATFORM_EXPORT ScrollbarTheme {
                               const IntRect&);
 
   virtual bool shouldCenterOnThumb(const ScrollbarThemeClient&,
-                                   const PlatformMouseEvent&);
+                                   const WebMouseEvent&);
   virtual bool shouldSnapBackToDragOrigin(const ScrollbarThemeClient&,
-                                          const PlatformMouseEvent&);
+                                          const WebMouseEvent&);
   virtual bool shouldDragDocumentInsteadOfThumb(const ScrollbarThemeClient&,
-                                                const PlatformMouseEvent&) {
+                                                const WebMouseEvent&) {
     return false;
   }
 
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollbarThemeAura.cpp b/third_party/WebKit/Source/platform/scroll/ScrollbarThemeAura.cpp
index ce7f749a4d7607..45c1d47b252270 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollbarThemeAura.cpp
+++ b/third_party/WebKit/Source/platform/scroll/ScrollbarThemeAura.cpp
@@ -31,7 +31,6 @@
 #include "platform/scroll/ScrollbarThemeAura.h"
 
 #include "platform/LayoutTestSupport.h"
-#include "platform/PlatformMouseEvent.h"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/graphics/GraphicsContext.h"
 #include "platform/graphics/paint/DrawingRecorder.h"
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollbarThemeMac.h b/third_party/WebKit/Source/platform/scroll/ScrollbarThemeMac.h
index 2dd3765738cd0d..558b170d04b573 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollbarThemeMac.h
+++ b/third_party/WebKit/Source/platform/scroll/ScrollbarThemeMac.h
@@ -89,7 +89,7 @@ class PLATFORM_EXPORT ScrollbarThemeMac : public ScrollbarTheme {
   int maxOverlapBetweenPages() override { return 40; }
 
   bool shouldDragDocumentInsteadOfThumb(const ScrollbarThemeClient&,
-                                        const PlatformMouseEvent&) override;
+                                        const WebMouseEvent&) override;
   int scrollbarPartToHIPressedState(ScrollbarPart);
 
   virtual void updateButtonPlacement(WebScrollbarButtonsPlacement) {}
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollbarThemeMac.mm b/third_party/WebKit/Source/platform/scroll/ScrollbarThemeMac.mm
index 88c92c377cb7d6..5fd9bd0d3af4ae 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollbarThemeMac.mm
+++ b/third_party/WebKit/Source/platform/scroll/ScrollbarThemeMac.mm
@@ -27,7 +27,6 @@
 #include "platform/scroll/ScrollbarThemeMac.h"
 
 #include <Carbon/Carbon.h>
-#include "platform/PlatformMouseEvent.h"
 #include "platform/graphics/GraphicsContext.h"
 #include "platform/graphics/GraphicsContextStateSaver.h"
 #include "platform/graphics/paint/DrawingRecorder.h"
@@ -36,6 +35,7 @@
 #include "platform/mac/NSScrollerImpDetails.h"
 #include "platform/mac/ScrollAnimatorMac.h"
 #include "platform/scroll/ScrollbarThemeClient.h"
+#include "public/platform/WebMouseEvent.h"
 #include "public/platform/WebThemeEngine.h"
 #include "public/platform/Platform.h"
 #include "public/platform/WebRect.h"
@@ -172,8 +172,8 @@ static bool supportsExpandedScrollbars() {
 
 bool ScrollbarThemeMac::shouldDragDocumentInsteadOfThumb(
     const ScrollbarThemeClient&,
-    const PlatformMouseEvent& event) {
-  return event.altKey();
+    const WebMouseEvent& event) {
+  return (event.modifiers() & WebInputEvent::Modifiers::AltKey) != 0;
 }
 
 int ScrollbarThemeMac::scrollbarPartToHIPressedState(ScrollbarPart part) {
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollbarThemeOverlay.cpp b/third_party/WebKit/Source/platform/scroll/ScrollbarThemeOverlay.cpp
index 14878b965bced5..9753dcc192827a 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollbarThemeOverlay.cpp
+++ b/third_party/WebKit/Source/platform/scroll/ScrollbarThemeOverlay.cpp
@@ -25,7 +25,6 @@
 
 #include "platform/scroll/ScrollbarThemeOverlay.h"
 
-#include "platform/PlatformMouseEvent.h"
 #include "platform/graphics/GraphicsContext.h"
 #include "platform/graphics/paint/DrawingRecorder.h"
 #include "platform/scroll/Scrollbar.h"
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollbarThemeOverlayMock.h b/third_party/WebKit/Source/platform/scroll/ScrollbarThemeOverlayMock.h
index 1022c2b2b1c47c..8f657e4b28dfdb 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollbarThemeOverlayMock.h
+++ b/third_party/WebKit/Source/platform/scroll/ScrollbarThemeOverlayMock.h
@@ -59,7 +59,7 @@ class PLATFORM_EXPORT ScrollbarThemeOverlayMock : public ScrollbarThemeOverlay {
   }
 
   bool shouldSnapBackToDragOrigin(const ScrollbarThemeClient& scrollbar,
-                                  const PlatformMouseEvent& evt) override {
+                                  const WebMouseEvent& evt) override {
     return false;
   }
 
diff --git a/third_party/WebKit/Source/web/AssertMatchingEnums.cpp b/third_party/WebKit/Source/web/AssertMatchingEnums.cpp
index dbfbb05a1ea7c8..3518f80b0f5045 100644
--- a/third_party/WebKit/Source/web/AssertMatchingEnums.cpp
+++ b/third_party/WebKit/Source/web/AssertMatchingEnums.cpp
@@ -66,7 +66,7 @@
 #include "platform/Cursor.h"
 #include "platform/FileMetadata.h"
 #include "platform/FileSystemType.h"
-#include "platform/PlatformMouseEvent.h"
+#include "platform/PlatformEvent.h"
 #include "platform/fonts/FontDescription.h"
 #include "platform/fonts/FontSmoothingMode.h"
 #include "platform/mediastream/MediaStreamSource.h"
diff --git a/third_party/WebKit/Source/web/InspectorOverlay.cpp b/third_party/WebKit/Source/web/InspectorOverlay.cpp
index 210ddea33e7fcf..4c14f4770d4d79 100644
--- a/third_party/WebKit/Source/web/InspectorOverlay.cpp
+++ b/third_party/WebKit/Source/web/InspectorOverlay.cpp
@@ -89,9 +89,11 @@ Node* hoveredNodeForEvent(LocalFrame* frame,
 }
 
 Node* hoveredNodeForEvent(LocalFrame* frame,
-                          const PlatformMouseEvent& event,
+                          const WebMouseEvent& event,
                           bool ignorePointerEventsNone) {
-  return hoveredNodeForPoint(frame, event.position(), ignorePointerEventsNone);
+  return hoveredNodeForPoint(frame,
+                             roundedIntPoint(event.positionInRootFrame()),
+                             ignorePointerEventsNone);
 }
 
 Node* hoveredNodeForEvent(LocalFrame* frame,
@@ -245,33 +247,30 @@ bool InspectorOverlay::handleInputEvent(const WebInputEvent& inputEvent) {
 
     overlayMainFrame()->eventHandler().handleGestureEvent(transformedEvent);
   }
-  if (WebInputEvent::isMouseEventType(inputEvent.type()) &&
-      inputEvent.type() != WebInputEvent::MouseEnter) {
-    // PlatformMouseEventBuilder does not work with MouseEnter type, so we
-    // filter it out manually.
-    PlatformMouseEvent mouseEvent = PlatformMouseEventBuilder(
-        m_frameImpl->frameView(),
-        static_cast<const WebMouseEvent&>(inputEvent));
+  if (WebInputEvent::isMouseEventType(inputEvent.type())) {
+    WebMouseEvent mouseEvent =
+        TransformWebMouseEvent(m_frameImpl->frameView(),
+                               static_cast<const WebMouseEvent&>(inputEvent));
 
-    if (mouseEvent.type() == PlatformEvent::MouseMoved)
+    if (mouseEvent.type() == WebInputEvent::MouseMove)
       handled = handleMouseMove(mouseEvent);
-    else if (mouseEvent.type() == PlatformEvent::MousePressed)
+    else if (mouseEvent.type() == WebInputEvent::MouseDown)
       handled = handleMousePress();
 
     if (handled)
       return true;
 
-    if (mouseEvent.type() == PlatformEvent::MouseMoved) {
+    if (mouseEvent.type() == WebInputEvent::MouseMove) {
       handled = overlayMainFrame()->eventHandler().handleMouseMoveEvent(
-                    mouseEvent, createPlatformMouseEventVector(
+                    mouseEvent, TransformWebMouseEventVector(
                                     m_frameImpl->frameView(),
                                     std::vector<const WebInputEvent*>())) !=
                 WebInputEventResult::NotHandled;
     }
-    if (mouseEvent.type() == PlatformEvent::MousePressed)
+    if (mouseEvent.type() == WebInputEvent::MouseDown)
       handled = overlayMainFrame()->eventHandler().handleMousePressEvent(
                     mouseEvent) != WebInputEventResult::NotHandled;
-    if (mouseEvent.type() == PlatformEvent::MouseReleased)
+    if (mouseEvent.type() == WebInputEvent::MouseUp)
       handled = overlayMainFrame()->eventHandler().handleMouseReleaseEvent(
                     mouseEvent) != WebInputEventResult::NotHandled;
   }
@@ -706,14 +705,15 @@ void InspectorOverlay::setShowViewportSizeOnResize(bool show) {
   m_drawViewSize = show;
 }
 
-bool InspectorOverlay::handleMouseMove(const PlatformMouseEvent& event) {
+bool InspectorOverlay::handleMouseMove(const WebMouseEvent& event) {
   if (!shouldSearchForNode())
     return false;
 
   LocalFrame* frame = m_frameImpl->frame();
   if (!frame || !frame->view() || frame->contentLayoutItem().isNull())
     return false;
-  Node* node = hoveredNodeForEvent(frame, event, event.shiftKey());
+  Node* node = hoveredNodeForEvent(frame, event,
+                                   event.modifiers() & WebInputEvent::ShiftKey);
 
   // Do not highlight within user agent shadow root unless requested.
   if (m_inspectMode != InspectorDOMAgent::SearchingForUAShadow) {
@@ -729,8 +729,9 @@ bool InspectorOverlay::handleMouseMove(const PlatformMouseEvent& event) {
   if (!node)
     return true;
 
-  Node* eventTarget =
-      event.shiftKey() ? hoveredNodeForEvent(frame, event, false) : nullptr;
+  Node* eventTarget = (event.modifiers() & WebInputEvent::ShiftKey)
+                          ? hoveredNodeForEvent(frame, event, false)
+                          : nullptr;
   if (eventTarget == node)
     eventTarget = nullptr;
 
@@ -739,7 +740,8 @@ bool InspectorOverlay::handleMouseMove(const PlatformMouseEvent& event) {
     if (m_domAgent)
       m_domAgent->nodeHighlightedInOverlay(node);
     highlightNode(node, eventTarget, *m_inspectModeHighlightConfig,
-                  event.ctrlKey() || event.metaKey());
+                  (event.modifiers() &
+                   (WebInputEvent::ControlKey | WebInputEvent::MetaKey)));
   }
   return true;
 }
diff --git a/third_party/WebKit/Source/web/InspectorOverlay.h b/third_party/WebKit/Source/web/InspectorOverlay.h
index a03cb44e0b2a10..7276894cfc848a 100644
--- a/third_party/WebKit/Source/web/InspectorOverlay.h
+++ b/third_party/WebKit/Source/web/InspectorOverlay.h
@@ -50,8 +50,8 @@ class LocalFrame;
 class Node;
 class Page;
 class PageOverlay;
-class PlatformMouseEvent;
 class WebGestureEvent;
+class WebMouseEvent;
 class WebLocalFrameImpl;
 class WebTouchEvent;
 
@@ -133,7 +133,7 @@ class InspectorOverlay final
   bool handleMousePress();
   bool handleGestureEvent(const WebGestureEvent&);
   bool handleTouchEvent(const WebTouchEvent&);
-  bool handleMouseMove(const PlatformMouseEvent&);
+  bool handleMouseMove(const WebMouseEvent&);
   bool shouldSearchForNode();
   void inspect(Node*);
 
diff --git a/third_party/WebKit/Source/web/PageWidgetDelegate.cpp b/third_party/WebKit/Source/web/PageWidgetDelegate.cpp
index bdc5f91a415ba4..a0fbb32574f133 100644
--- a/third_party/WebKit/Source/web/PageWidgetDelegate.cpp
+++ b/third_party/WebKit/Source/web/PageWidgetDelegate.cpp
@@ -119,10 +119,11 @@ WebInputEventResult PageWidgetDelegate::handleInputEvent(
   const WebInputEvent& event = coalescedEvent.event();
   if (event.modifiers() & WebInputEvent::IsTouchAccessibility &&
       WebInputEvent::isMouseEventType(event.type())) {
-    PlatformMouseEventBuilder pme(root->view(),
-                                  static_cast<const WebMouseEvent&>(event));
+    WebMouseEvent mouseEvent = TransformWebMouseEvent(
+        root->view(), static_cast<const WebMouseEvent&>(event));
 
-    IntPoint docPoint(root->view()->rootFrameToContents(pme.position()));
+    IntPoint docPoint(root->view()->rootFrameToContents(
+        flooredIntPoint(mouseEvent.positionInRootFrame())));
     HitTestResult result = root->eventHandler().hitTestResultAtPoint(
         docPoint, HitTestRequest::ReadOnly | HitTestRequest::Active);
     result.setToShadowHostIfInUserAgentShadowRoot();
@@ -225,27 +226,32 @@ void PageWidgetEventHandler::handleMouseMove(
     LocalFrame& mainFrame,
     const WebMouseEvent& event,
     const std::vector<const WebInputEvent*>& coalescedEvents) {
+  WebMouseEvent transformedEvent =
+      TransformWebMouseEvent(mainFrame.view(), event);
   mainFrame.eventHandler().handleMouseMoveEvent(
-      PlatformMouseEventBuilder(mainFrame.view(), event),
-      createPlatformMouseEventVector(mainFrame.view(), coalescedEvents));
+      transformedEvent,
+      TransformWebMouseEventVector(mainFrame.view(), coalescedEvents));
 }
 
 void PageWidgetEventHandler::handleMouseLeave(LocalFrame& mainFrame,
                                               const WebMouseEvent& event) {
-  mainFrame.eventHandler().handleMouseLeaveEvent(
-      PlatformMouseEventBuilder(mainFrame.view(), event));
+  WebMouseEvent transformedEvent =
+      TransformWebMouseEvent(mainFrame.view(), event);
+  mainFrame.eventHandler().handleMouseLeaveEvent(transformedEvent);
 }
 
 void PageWidgetEventHandler::handleMouseDown(LocalFrame& mainFrame,
                                              const WebMouseEvent& event) {
-  mainFrame.eventHandler().handleMousePressEvent(
-      PlatformMouseEventBuilder(mainFrame.view(), event));
+  WebMouseEvent transformedEvent =
+      TransformWebMouseEvent(mainFrame.view(), event);
+  mainFrame.eventHandler().handleMousePressEvent(transformedEvent);
 }
 
 void PageWidgetEventHandler::handleMouseUp(LocalFrame& mainFrame,
                                            const WebMouseEvent& event) {
-  mainFrame.eventHandler().handleMouseReleaseEvent(
-      PlatformMouseEventBuilder(mainFrame.view(), event));
+  WebMouseEvent transformedEvent =
+      TransformWebMouseEvent(mainFrame.view(), event);
+  mainFrame.eventHandler().handleMouseReleaseEvent(transformedEvent);
 }
 
 WebInputEventResult PageWidgetEventHandler::handleMouseWheel(
diff --git a/third_party/WebKit/Source/web/PopupMenuImpl.cpp b/third_party/WebKit/Source/web/PopupMenuImpl.cpp
index 7b2b88f4b059ea..97bf482a6c9ff1 100644
--- a/third_party/WebKit/Source/web/PopupMenuImpl.cpp
+++ b/third_party/WebKit/Source/web/PopupMenuImpl.cpp
@@ -446,7 +446,9 @@ void PopupMenuImpl::setValueAndClosePopup(int numValue,
   // We dispatch events on the owner element to match the legacy behavior.
   // Other browsers dispatch click events before and after showing the popup.
   if (m_ownerElement) {
-    PlatformMouseEvent event;
+    // TODO(dtapuska): Why is this event positionless?
+    WebMouseEvent event;
+    event.setFrameScale(1);
     Element* owner = &ownerElement();
     owner->dispatchMouseEvent(event, EventTypeNames::mouseup);
     owner->dispatchMouseEvent(event, EventTypeNames::click);
diff --git a/third_party/WebKit/Source/web/WebDevToolsAgentImpl.cpp b/third_party/WebKit/Source/web/WebDevToolsAgentImpl.cpp
index 8ff5670b996beb..2f1df5b1efa90b 100644
--- a/third_party/WebKit/Source/web/WebDevToolsAgentImpl.cpp
+++ b/third_party/WebKit/Source/web/WebDevToolsAgentImpl.cpp
@@ -540,9 +540,9 @@ void WebDevToolsAgentImpl::inspectElementAt(int sessionId,
                            WTF::monotonicallyIncreasingTimeMS());
   dummyEvent.x = pointInRootFrame.x;
   dummyEvent.y = pointInRootFrame.y;
-  IntPoint transformedPoint =
-      PlatformMouseEventBuilder(m_webLocalFrameImpl->frameView(), dummyEvent)
-          .position();
+  IntPoint transformedPoint = flooredIntPoint(
+      TransformWebMouseEvent(m_webLocalFrameImpl->frameView(), dummyEvent)
+          .positionInRootFrame());
   HitTestResult result(
       request,
       m_webLocalFrameImpl->frameView()->rootFrameToContents(transformedPoint));
diff --git a/third_party/WebKit/Source/web/WebFrameWidgetBase.cpp b/third_party/WebKit/Source/web/WebFrameWidgetBase.cpp
index 00a0c73407b793..5a34a0e3281039 100644
--- a/third_party/WebKit/Source/web/WebFrameWidgetBase.cpp
+++ b/third_party/WebKit/Source/web/WebFrameWidgetBase.cpp
@@ -131,16 +131,19 @@ void WebFrameWidgetBase::dragSourceEndedAt(const WebPoint& pointInViewport,
     cancelDrag();
     return;
   }
-  WebPoint pointInRootFrame(
+  WebFloatPoint pointInRootFrame(
       page()->frameHost().visualViewport().viewportToRootFrame(
           pointInViewport));
-  PlatformMouseEvent pme(
-      pointInRootFrame, screenPoint, WebPointerProperties::Button::Left,
-      PlatformEvent::MouseMoved, 0, PlatformEvent::NoModifiers,
-      PlatformMouseEvent::RealOrIndistinguishable, TimeTicks::Now());
+
+  WebMouseEvent fakeMouseMove(WebInputEvent::MouseMove, pointInRootFrame,
+                              WebFloatPoint(screenPoint.x, screenPoint.y),
+                              WebPointerProperties::Button::Left, 0,
+                              PlatformEvent::NoModifiers,
+                              TimeTicks::Now().InSeconds());
+  fakeMouseMove.setFrameScale(1);
   toCoreFrame(localRoot())
       ->eventHandler()
-      .dragSourceEndedAt(pme, static_cast<DragOperation>(operation));
+      .dragSourceEndedAt(fakeMouseMove, static_cast<DragOperation>(operation));
 }
 
 void WebFrameWidgetBase::dragSourceSystemDragEnded() {
diff --git a/third_party/WebKit/Source/web/WebFrameWidgetImpl.cpp b/third_party/WebKit/Source/web/WebFrameWidgetImpl.cpp
index 563b887b646c93..b015b9b24c3c74 100644
--- a/third_party/WebKit/Source/web/WebFrameWidgetImpl.cpp
+++ b/third_party/WebKit/Source/web/WebFrameWidgetImpl.cpp
@@ -372,11 +372,11 @@ WebInputEventResult WebFrameWidgetImpl::handleInputEvent(
         NOTREACHED();
     }
 
-    node->dispatchMouseEvent(
-        PlatformMouseEventBuilder(
-            m_localRoot->frameView(),
-            static_cast<const WebMouseEvent&>(inputEvent)),
-        eventType, static_cast<const WebMouseEvent&>(inputEvent).clickCount);
+    WebMouseEvent transformedEvent =
+        TransformWebMouseEvent(m_localRoot->frameView(),
+                               static_cast<const WebMouseEvent&>(inputEvent));
+    node->dispatchMouseEvent(transformedEvent, eventType,
+                             transformedEvent.clickCount);
     return WebInputEventResult::HandledSystem;
   }
 
@@ -776,10 +776,13 @@ void WebFrameWidgetImpl::handleMouseDown(LocalFrame& mainFrame,
 void WebFrameWidgetImpl::mouseContextMenu(const WebMouseEvent& event) {
   page()->contextMenuController().clearContextMenu();
 
-  PlatformMouseEventBuilder pme(m_localRoot->frameView(), event);
+  WebMouseEvent transformedEvent =
+      TransformWebMouseEvent(m_localRoot->frameView(), event);
+  IntPoint positionInRootFrame =
+      flooredIntPoint(transformedEvent.positionInRootFrame());
 
   // Find the right target frame. See issue 1186900.
-  HitTestResult result = hitTestResultForRootFramePos(pme.position());
+  HitTestResult result = hitTestResultForRootFramePos(positionInRootFrame);
   Frame* targetFrame;
   if (result.innerNodeOrImageMapImage())
     targetFrame = result.innerNodeOrImageMapImage()->document().frame();
@@ -801,7 +804,8 @@ void WebFrameWidgetImpl::mouseContextMenu(const WebMouseEvent& event) {
 
   {
     ContextMenuAllowedScope scope;
-    targetLocalFrame->eventHandler().sendContextMenuEvent(pme, nullptr);
+    targetLocalFrame->eventHandler().sendContextMenuEvent(transformedEvent,
+                                                          nullptr);
   }
   // Actually showing the context menu is handled by the ContextMenuClient
   // implementation...
diff --git a/third_party/WebKit/Source/web/WebInputEventConversion.cpp b/third_party/WebKit/Source/web/WebInputEventConversion.cpp
index aed825ce918ec8..4c585682ed8dd3 100644
--- a/third_party/WebKit/Source/web/WebInputEventConversion.cpp
+++ b/third_party/WebKit/Source/web/WebInputEventConversion.cpp
@@ -85,54 +85,6 @@ FloatPoint frameTranslation(const Widget* widget) {
           overscrollOffset.height());
 }
 
-float scaleDeltaToWindow(const Widget* widget, float delta) {
-  return delta / frameScale(widget);
-}
-
-// This method converts from the renderer's coordinate space into Blink's root
-// frame coordinate space.  It's somewhat unique in that it takes into account
-// DevTools emulation, which applies a scale and offset in the root layer (see
-// updateRootLayerTransform in WebViewImpl) as well as the overscroll effect on
-// OSX.  This is in addition to the visual viewport "pinch-zoom" transformation
-// and is one of the few cases where the visual viewport is not equal to the
-// renderer's coordinate-space.
-FloatPoint convertHitPointToRootFrame(const Widget* widget,
-                                      FloatPoint pointInRendererViewport) {
-  float scale = 1;
-  IntSize offset;
-  IntPoint visualViewport;
-  FloatSize overscrollOffset;
-  if (widget) {
-    FrameView* rootView = toFrameView(widget->root());
-    if (rootView) {
-      scale = rootView->inputEventsScaleFactor();
-      offset = rootView->inputEventsOffsetForEmulation();
-      visualViewport = flooredIntPoint(rootView->page()
-                                           ->frameHost()
-                                           .visualViewport()
-                                           .visibleRect()
-                                           .location());
-      overscrollOffset =
-          rootView->page()->frameHost().chromeClient().elasticOverscroll();
-    }
-  }
-  return FloatPoint((pointInRendererViewport.x() - offset.width()) / scale +
-                        visualViewport.x() + overscrollOffset.width(),
-                    (pointInRendererViewport.y() - offset.height()) / scale +
-                        visualViewport.y() + overscrollOffset.height());
-}
-
-unsigned toPlatformModifierFrom(WebMouseEvent::Button button) {
-  if (button == WebMouseEvent::Button::NoButton)
-    return 0;
-
-  unsigned webMouseButtonToPlatformModifier[] = {
-      PlatformEvent::LeftButtonDown, PlatformEvent::MiddleButtonDown,
-      PlatformEvent::RightButtonDown};
-
-  return webMouseButtonToPlatformModifier[static_cast<int>(button)];
-}
-
 FloatPoint convertAbsoluteLocationForLayoutObjectFloat(
     const DoublePoint& location,
     const LayoutItem layoutItem) {
@@ -172,51 +124,40 @@ void updateWebMouseEventFromCoreMouseEvent(const MouseEvent& event,
   webEvent.y = localPoint.y();
 }
 
-}  // namespace
+unsigned toWebInputEventModifierFrom(WebMouseEvent::Button button) {
+  if (button == WebMouseEvent::Button::NoButton)
+    return 0;
 
-// MakePlatformMouseEvent -----------------------------------------------------
-
-// TODO(mustaq): Add tests for this.
-PlatformMouseEventBuilder::PlatformMouseEventBuilder(Widget* widget,
-                                                     const WebMouseEvent& e) {
-  // FIXME: Widget is always toplevel, unless it's a popup. We may be able
-  // to get rid of this once we abstract popups into a WebKit API.
-  m_position = widget->convertFromRootFrame(
-      flooredIntPoint(convertHitPointToRootFrame(widget, IntPoint(e.x, e.y))));
-  m_globalPosition = IntPoint(e.globalX, e.globalY);
-  m_movementDelta = IntPoint(scaleDeltaToWindow(widget, e.movementX),
-                             scaleDeltaToWindow(widget, e.movementY));
-  m_modifiers = e.modifiers();
-
-  m_timestamp = TimeTicks::FromSeconds(e.timeStampSeconds());
-  m_clickCount = e.clickCount;
-
-  m_pointerProperties = static_cast<WebPointerProperties>(e);
-
-  switch (e.type()) {
-    case WebInputEvent::MouseMove:
-    case WebInputEvent::MouseEnter:  // synthesize a move event
-    case WebInputEvent::MouseLeave:  // synthesize a move event
-      m_type = PlatformEvent::MouseMoved;
-      break;
+  unsigned webMouseButtonToPlatformModifier[] = {
+      WebInputEvent::LeftButtonDown, WebInputEvent::MiddleButtonDown,
+      WebInputEvent::RightButtonDown};
 
-    case WebInputEvent::MouseDown:
-      m_type = PlatformEvent::MousePressed;
-      break;
+  return webMouseButtonToPlatformModifier[static_cast<int>(button)];
+}
 
-    case WebInputEvent::MouseUp:
-      m_type = PlatformEvent::MouseReleased;
+}  // namespace
 
-      // The MouseEvent spec requires that buttons indicates the state
-      // immediately after the event takes place. To ensure consistency
-      // between platforms here, we explicitly clear the button that is
-      // in the process of being released.
-      m_modifiers &= ~toPlatformModifierFrom(e.button);
-      break;
+WebMouseEvent TransformWebMouseEvent(Widget* widget,
+                                     const WebMouseEvent& event) {
+  WebMouseEvent result = event;
 
-    default:
-      NOTREACHED();
+  // TODO(dtapuska): Remove this translation. In the past blink has
+  // converted leaves into moves and not known about leaves. It should
+  // be educated about them. crbug.com/686196
+  if (event.type() == WebInputEvent::MouseEnter ||
+      event.type() == WebInputEvent::MouseLeave) {
+    result.setType(WebInputEvent::MouseMove);
   }
+
+  // TODO(dtapuska): Perhaps the event should be constructed correctly?
+  // crbug.com/686200
+  if (event.type() == WebInputEvent::MouseUp) {
+    result.setModifiers(event.modifiers() &
+                        ~toWebInputEventModifierFrom(event.button));
+  }
+  result.setFrameScale(frameScale(widget));
+  result.setFrameTranslate(frameTranslation(widget));
+  return result;
 }
 
 WebMouseWheelEvent TransformWebMouseWheelEvent(
@@ -258,6 +199,21 @@ WebTouchEvent TransformWebTouchEvent(Widget* widget,
 WebMouseEventBuilder::WebMouseEventBuilder(const Widget* widget,
                                            const LayoutItem layoutItem,
                                            const MouseEvent& event) {
+  if (event.nativeEvent()) {
+    *static_cast<WebMouseEvent*>(this) =
+        event.nativeEvent()->flattenTransform();
+    WebFloatPoint absoluteRootFrameLocation = positionInRootFrame();
+    IntPoint localPoint = roundedIntPoint(
+        layoutItem.absoluteToLocal(absoluteRootFrameLocation, UseTransforms));
+    x = localPoint.x();
+    y = localPoint.y();
+    return;
+  }
+
+  // Code below here can be removed once OOPIF ships.
+  // OOPIF will prevent synthetic events being dispatched into
+  // other frames; but for now we allow the fallback to generate
+  // WebMouseEvents from synthetic events.
   if (event.type() == EventTypeNames::mousemove)
     m_type = WebInputEvent::MouseMove;
   else if (event.type() == EventTypeNames::mouseout)
@@ -308,8 +264,6 @@ WebMouseEventBuilder::WebMouseEventBuilder(const Widget* widget,
   clickCount = event.detail();
 
   pointerType = WebPointerProperties::PointerType::Mouse;
-  if (event.mouseEvent())
-    pointerType = event.mouseEvent()->pointerProperties().pointerType;
 }
 
 // Generate a synthetic WebMouseEvent given a TouchEvent (eg. for emulating a
@@ -396,13 +350,13 @@ WebKeyboardEventBuilder::WebKeyboardEventBuilder(const KeyboardEvent& event) {
   windowsKeyCode = event.keyCode();
 }
 
-Vector<PlatformMouseEvent> createPlatformMouseEventVector(
+Vector<WebMouseEvent> TransformWebMouseEventVector(
     Widget* widget,
     const std::vector<const WebInputEvent*>& coalescedEvents) {
-  Vector<PlatformMouseEvent> result;
+  Vector<WebMouseEvent> result;
   for (const auto& event : coalescedEvents) {
     DCHECK(WebInputEvent::isMouseEventType(event->type()));
-    result.push_back(PlatformMouseEventBuilder(
+    result.push_back(TransformWebMouseEvent(
         widget, static_cast<const WebMouseEvent&>(*event)));
   }
   return result;
diff --git a/third_party/WebKit/Source/web/WebInputEventConversion.h b/third_party/WebKit/Source/web/WebInputEventConversion.h
index f2972ec3c692c6..0d4878361ab98a 100644
--- a/third_party/WebKit/Source/web/WebInputEventConversion.h
+++ b/third_party/WebKit/Source/web/WebInputEventConversion.h
@@ -31,7 +31,6 @@
 #ifndef WebInputEventConversion_h
 #define WebInputEventConversion_h
 
-#include "platform/PlatformMouseEvent.h"
 #include "platform/scroll/ScrollTypes.h"
 #include "public/platform/WebInputEvent.h"
 #include "public/platform/WebKeyboardEvent.h"
@@ -48,19 +47,12 @@ class MouseEvent;
 class LayoutItem;
 class TouchEvent;
 class WebGestureEvent;
-class WebMouseEvent;
 class WebKeyboardEvent;
-class WebTouchEvent;
 class Widget;
 
 // These classes are used to convert from WebInputEvent subclasses to
 // corresponding WebCore events.
 
-class WEB_EXPORT PlatformMouseEventBuilder
-    : NON_EXPORTED_BASE(public PlatformMouseEvent) {
- public:
-  PlatformMouseEventBuilder(Widget*, const WebMouseEvent&);
-};
 
 class WEB_EXPORT WebMouseEventBuilder
     : NON_EXPORTED_BASE(public WebMouseEvent) {
@@ -96,14 +88,15 @@ class WEB_EXPORT WebTouchEventBuilder
 // and translation.
 WEB_EXPORT WebGestureEvent TransformWebGestureEvent(Widget*,
                                                     const WebGestureEvent&);
+WEB_EXPORT WebMouseEvent TransformWebMouseEvent(Widget*, const WebMouseEvent&);
+
 WEB_EXPORT WebMouseWheelEvent
 TransformWebMouseWheelEvent(Widget*, const WebMouseWheelEvent&);
 
 WEB_EXPORT WebTouchEvent TransformWebTouchEvent(Widget*, const WebTouchEvent&);
 
-Vector<PlatformMouseEvent> WEB_EXPORT
-createPlatformMouseEventVector(Widget*,
-                               const std::vector<const WebInputEvent*>&);
+Vector<WebMouseEvent> WEB_EXPORT
+TransformWebMouseEventVector(Widget*, const std::vector<const WebInputEvent*>&);
 Vector<WebTouchEvent> WEB_EXPORT
 TransformWebTouchEventVector(Widget*, const std::vector<const WebInputEvent*>&);
 
diff --git a/third_party/WebKit/Source/web/WebPluginContainerImpl.cpp b/third_party/WebKit/Source/web/WebPluginContainerImpl.cpp
index 865ab971dcd5c3..00617d0b41d1c4 100644
--- a/third_party/WebKit/Source/web/WebPluginContainerImpl.cpp
+++ b/third_party/WebKit/Source/web/WebPluginContainerImpl.cpp
@@ -706,16 +706,16 @@ void WebPluginContainerImpl::handleMouseEvent(MouseEvent* event) {
   // in the call to HandleEvent. See http://b/issue?id=1362948
   FrameView* parentView = toFrameView(parent());
 
-  WebMouseEventBuilder webEvent(this, LayoutItem(m_element->layoutObject()),
-                                *event);
-  if (webEvent.type() == WebInputEvent::Undefined)
+  WebMouseEventBuilder transformedEvent(
+      this, LayoutItem(m_element->layoutObject()), *event);
+  if (transformedEvent.type() == WebInputEvent::Undefined)
     return;
 
   if (event->type() == EventTypeNames::mousedown)
     focusPlugin();
 
   WebCursorInfo cursorInfo;
-  if (m_webPlugin->handleInputEvent(webEvent, cursorInfo) !=
+  if (m_webPlugin->handleInputEvent(transformedEvent, cursorInfo) !=
       WebInputEventResult::NotHandled)
     event->setDefaultHandled();
 
diff --git a/third_party/WebKit/Source/web/WebViewImpl.cpp b/third_party/WebKit/Source/web/WebViewImpl.cpp
index fe119164d3f4f1..ddc23b9cacb0e3 100644
--- a/third_party/WebKit/Source/web/WebViewImpl.cpp
+++ b/third_party/WebKit/Source/web/WebViewImpl.cpp
@@ -97,7 +97,6 @@
 #include "platform/Cursor.h"
 #include "platform/Histogram.h"
 #include "platform/KeyboardCodes.h"
-#include "platform/PlatformMouseEvent.h"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/UserGestureIndicator.h"
 #include "platform/animation/CompositorAnimationHost.h"
@@ -556,10 +555,13 @@ void WebViewImpl::mouseContextMenu(const WebMouseEvent& event) {
 
   m_page->contextMenuController().clearContextMenu();
 
-  PlatformMouseEventBuilder pme(mainFrameImpl()->frameView(), event);
+  WebMouseEvent transformedEvent =
+      TransformWebMouseEvent(mainFrameImpl()->frameView(), event);
+  IntPoint positionInRootFrame =
+      flooredIntPoint(transformedEvent.positionInRootFrame());
 
   // Find the right target frame. See issue 1186900.
-  HitTestResult result = hitTestResultForRootFramePos(pme.position());
+  HitTestResult result = hitTestResultForRootFramePos(positionInRootFrame);
   Frame* targetFrame;
   if (result.innerNodeOrImageMapImage())
     targetFrame = result.innerNodeOrImageMapImage()->document().frame();
@@ -577,7 +579,8 @@ void WebViewImpl::mouseContextMenu(const WebMouseEvent& event) {
 
   {
     ContextMenuAllowedScope scope;
-    targetLocalFrame->eventHandler().sendContextMenuEvent(pme, nullptr);
+    targetLocalFrame->eventHandler().sendContextMenuEvent(transformedEvent,
+                                                          nullptr);
   }
   // Actually showing the context menu is handled by the ContextMenuClient
   // implementation...
@@ -2189,11 +2192,11 @@ WebInputEventResult WebViewImpl::handleInputEvent(
         NOTREACHED();
     }
 
-    node->dispatchMouseEvent(
-        PlatformMouseEventBuilder(
-            mainFrameImpl()->frameView(),
-            static_cast<const WebMouseEvent&>(inputEvent)),
-        eventType, static_cast<const WebMouseEvent&>(inputEvent).clickCount);
+    WebMouseEvent transformedEvent =
+        TransformWebMouseEvent(mainFrameImpl()->frameView(),
+                               static_cast<const WebMouseEvent&>(inputEvent));
+    node->dispatchMouseEvent(transformedEvent, eventType,
+                             transformedEvent.clickCount);
     return WebInputEventResult::HandledSystem;
   }
 
@@ -4125,10 +4128,12 @@ void WebViewImpl::pointerLockMouseEvent(const WebInputEvent& event) {
 
   const WebMouseEvent& mouseEvent = static_cast<const WebMouseEvent&>(event);
 
-  if (page())
-    page()->pointerLockController().dispatchLockedMouseEvent(
-        PlatformMouseEventBuilder(mainFrameImpl()->frameView(), mouseEvent),
-        eventType);
+  if (page()) {
+    WebMouseEvent transformedEvent =
+        TransformWebMouseEvent(mainFrameImpl()->frameView(), mouseEvent);
+    page()->pointerLockController().dispatchLockedMouseEvent(transformedEvent,
+                                                             eventType);
+  }
 }
 
 void WebViewImpl::forceNextWebGLContextCreationToFail() {
diff --git a/third_party/WebKit/Source/web/tests/WebFrameTest.cpp b/third_party/WebKit/Source/web/tests/WebFrameTest.cpp
index f07cc25b0229d6..d123a03ceffb17 100644
--- a/third_party/WebKit/Source/web/tests/WebFrameTest.cpp
+++ b/third_party/WebKit/Source/web/tests/WebFrameTest.cpp
@@ -79,7 +79,6 @@
 #include "modules/mediastream/MediaStreamRegistry.h"
 #include "platform/Cursor.h"
 #include "platform/DragImage.h"
-#include "platform/PlatformMouseEvent.h"
 #include "platform/PlatformResourceLoader.h"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/UserGestureIndicator.h"
@@ -6873,10 +6872,12 @@ TEST_P(ParameterizedWebFrameTest, SimulateFragmentAnchorMiddleClick) {
   KURL destination = document->url();
   destination.setFragmentIdentifier("test");
 
-  Event* event = MouseEvent::create(
-      EventTypeNames::click, false, false, document->domWindow(), 0, 0, 0, 0, 0,
-      0, 0, PlatformEvent::NoModifiers, 1, 0, nullptr, TimeTicks(),
-      PlatformMouseEvent::RealOrIndistinguishable, String(), nullptr);
+  MouseEventInit mouseInitializer;
+  mouseInitializer.setView(document->domWindow());
+  mouseInitializer.setButton(1);
+
+  Event* event =
+      MouseEvent::create(nullptr, EventTypeNames::click, mouseInitializer);
   FrameLoadRequest frameRequest(document, ResourceRequest(destination));
   frameRequest.setTriggeringEvent(event);
   toLocalFrame(webViewHelper.webView()->page()->mainFrame())
@@ -6928,10 +6929,13 @@ TEST_P(ParameterizedWebFrameTest, ModifiedClickNewWindow) {
   KURL destination = toKURL(m_baseURL + "hello_world.html");
 
   // ctrl+click event
-  Event* event = MouseEvent::create(
-      EventTypeNames::click, false, false, document->domWindow(), 0, 0, 0, 0, 0,
-      0, 0, PlatformEvent::CtrlKey, 0, 0, nullptr, TimeTicks(),
-      PlatformMouseEvent::RealOrIndistinguishable, String(), nullptr);
+  MouseEventInit mouseInitializer;
+  mouseInitializer.setView(document->domWindow());
+  mouseInitializer.setButton(1);
+  mouseInitializer.setCtrlKey(true);
+
+  Event* event =
+      MouseEvent::create(nullptr, EventTypeNames::click, mouseInitializer);
   FrameLoadRequest frameRequest(document, ResourceRequest(destination));
   frameRequest.setTriggeringEvent(event);
   UserGestureIndicator gesture(DocumentUserGestureToken::create(document));
@@ -10795,13 +10799,15 @@ TEST_F(WebFrameTest, MouseOverDifferntNodeClearsTooltip) {
   EXPECT_TRUE(hitTestResult.innerElement());
 
   // Mouse over link. Mouse cursor should be hand.
-  PlatformMouseEvent mouseMoveOverLinkEvent(
-      IntPoint(div1Tag->offsetLeft() + 5, div1Tag->offsetTop() + 5),
-      IntPoint(div1Tag->offsetLeft() + 5, div1Tag->offsetTop() + 5),
-      WebPointerProperties::Button::NoButton, PlatformEvent::MouseMoved, 0,
-      PlatformEvent::NoModifiers, TimeTicks::Now());
+  WebMouseEvent mouseMoveOverLinkEvent(
+      WebInputEvent::MouseMove,
+      WebFloatPoint(div1Tag->offsetLeft() + 5, div1Tag->offsetTop() + 5),
+      WebFloatPoint(div1Tag->offsetLeft() + 5, div1Tag->offsetTop() + 5),
+      WebPointerProperties::Button::NoButton, 0, WebInputEvent::NoModifiers,
+      TimeTicks::Now().InSeconds());
+  mouseMoveOverLinkEvent.setFrameScale(1);
   document->frame()->eventHandler().handleMouseMoveEvent(
-      mouseMoveOverLinkEvent, Vector<PlatformMouseEvent>());
+      mouseMoveOverLinkEvent, Vector<WebMouseEvent>());
 
   EXPECT_EQ(document->hoverNode(),
             document->frame()->chromeClient().lastSetTooltipNodeForTesting());
@@ -10810,13 +10816,15 @@ TEST_F(WebFrameTest, MouseOverDifferntNodeClearsTooltip) {
 
   Element* div2Tag = document->getElementById("div2");
 
-  PlatformMouseEvent mouseMoveEvent(
-      IntPoint(div2Tag->offsetLeft() + 5, div2Tag->offsetTop() + 5),
-      IntPoint(div2Tag->offsetLeft() + 5, div2Tag->offsetTop() + 5),
-      WebPointerProperties::Button::NoButton, PlatformEvent::MouseMoved, 0,
-      PlatformEvent::NoModifiers, TimeTicks::Now());
+  WebMouseEvent mouseMoveEvent(
+      WebInputEvent::MouseMove,
+      WebFloatPoint(div2Tag->offsetLeft() + 5, div2Tag->offsetTop() + 5),
+      WebFloatPoint(div2Tag->offsetLeft() + 5, div2Tag->offsetTop() + 5),
+      WebPointerProperties::Button::NoButton, 0, WebInputEvent::NoModifiers,
+      TimeTicks::Now().InSeconds());
+  mouseMoveEvent.setFrameScale(1);
   document->frame()->eventHandler().handleMouseMoveEvent(
-      mouseMoveEvent, Vector<PlatformMouseEvent>());
+      mouseMoveEvent, Vector<WebMouseEvent>());
 
   EXPECT_EQ(document->hoverNode(),
             document->frame()->chromeClient().lastSetTooltipNodeForTesting());
@@ -10857,13 +10865,15 @@ TEST_F(WebFrameTest, MouseOverLinkAndOverlayScrollbar) {
   EXPECT_FALSE(hitTestResult.scrollbar()->isCustomScrollbar());
 
   // Mouse over link. Mouse cursor should be hand.
-  PlatformMouseEvent mouseMoveOverLinkEvent(
-      IntPoint(aTag->offsetLeft(), aTag->offsetTop()),
-      IntPoint(aTag->offsetLeft(), aTag->offsetTop()),
-      WebPointerProperties::Button::NoButton, PlatformEvent::MouseMoved, 0,
-      PlatformEvent::NoModifiers, TimeTicks::Now());
+  WebMouseEvent mouseMoveOverLinkEvent(
+      WebInputEvent::MouseMove,
+      WebFloatPoint(aTag->offsetLeft(), aTag->offsetTop()),
+      WebFloatPoint(aTag->offsetLeft(), aTag->offsetTop()),
+      WebPointerProperties::Button::NoButton, 0, WebInputEvent::NoModifiers,
+      TimeTicks::Now().InSeconds());
+  mouseMoveOverLinkEvent.setFrameScale(1);
   document->frame()->eventHandler().handleMouseMoveEvent(
-      mouseMoveOverLinkEvent, Vector<PlatformMouseEvent>());
+      mouseMoveOverLinkEvent, Vector<WebMouseEvent>());
 
   EXPECT_EQ(
       Cursor::Type::Hand,
@@ -10871,31 +10881,37 @@ TEST_F(WebFrameTest, MouseOverLinkAndOverlayScrollbar) {
 
   // Mouse over enabled overlay scrollbar. Mouse cursor should be pointer and no
   // active hover element.
-  PlatformMouseEvent mouseMoveEvent(
-      IntPoint(18, aTag->offsetTop()), IntPoint(18, aTag->offsetTop()),
-      WebPointerProperties::Button::NoButton, PlatformEvent::MouseMoved, 0,
-      PlatformEvent::NoModifiers, TimeTicks::Now());
+  WebMouseEvent mouseMoveEvent(
+      WebInputEvent::MouseMove, WebFloatPoint(18, aTag->offsetTop()),
+      WebFloatPoint(18, aTag->offsetTop()),
+      WebPointerProperties::Button::NoButton, 0, WebInputEvent::NoModifiers,
+      TimeTicks::Now().InSeconds());
+  mouseMoveEvent.setFrameScale(1);
   document->frame()->eventHandler().handleMouseMoveEvent(
-      mouseMoveEvent, Vector<PlatformMouseEvent>());
+      mouseMoveEvent, Vector<WebMouseEvent>());
 
   EXPECT_EQ(
       Cursor::Type::Pointer,
       document->frame()->chromeClient().lastSetCursorForTesting().getType());
 
-  PlatformMouseEvent mousePressEvent(
-      IntPoint(18, aTag->offsetTop()), IntPoint(18, aTag->offsetTop()),
-      WebPointerProperties::Button::Left, PlatformEvent::MousePressed, 0,
-      PlatformEvent::Modifiers::LeftButtonDown, TimeTicks::Now());
+  WebMouseEvent mousePressEvent(
+      WebInputEvent::MouseDown, WebFloatPoint(18, aTag->offsetTop()),
+      WebFloatPoint(18, aTag->offsetTop()), WebPointerProperties::Button::Left,
+      0, WebInputEvent::Modifiers::LeftButtonDown,
+      TimeTicks::Now().InSeconds());
+  mousePressEvent.setFrameScale(1);
   document->frame()->eventHandler().handleMousePressEvent(mousePressEvent);
 
   EXPECT_FALSE(document->activeHoverElement());
   EXPECT_FALSE(document->hoverNode());
 
-  PlatformMouseEvent MouseReleaseEvent(
-      IntPoint(18, aTag->offsetTop()), IntPoint(18, aTag->offsetTop()),
-      WebPointerProperties::Button::Left, PlatformEvent::MouseReleased, 0,
-      PlatformEvent::Modifiers::LeftButtonDown, TimeTicks::Now());
-  document->frame()->eventHandler().handleMouseReleaseEvent(MouseReleaseEvent);
+  WebMouseEvent mouseReleaseEvent(
+      WebInputEvent::MouseUp, WebFloatPoint(18, aTag->offsetTop()),
+      WebFloatPoint(18, aTag->offsetTop()), WebPointerProperties::Button::Left,
+      0, WebInputEvent::Modifiers::LeftButtonDown,
+      TimeTicks::Now().InSeconds());
+  mouseReleaseEvent.setFrameScale(1);
+  document->frame()->eventHandler().handleMouseReleaseEvent(mouseReleaseEvent);
 
   // Mouse over disabled overlay scrollbar. Mouse cursor should be hand and has
   // active hover element.
@@ -10909,7 +10925,7 @@ TEST_F(WebFrameTest, MouseOverLinkAndOverlayScrollbar) {
   EXPECT_FALSE(hitTestResult.scrollbar());
 
   document->frame()->eventHandler().handleMouseMoveEvent(
-      mouseMoveEvent, Vector<PlatformMouseEvent>());
+      mouseMoveEvent, Vector<WebMouseEvent>());
 
   EXPECT_EQ(
       Cursor::Type::Hand,
@@ -10920,7 +10936,7 @@ TEST_F(WebFrameTest, MouseOverLinkAndOverlayScrollbar) {
   EXPECT_TRUE(document->activeHoverElement());
   EXPECT_TRUE(document->hoverNode());
 
-  document->frame()->eventHandler().handleMouseReleaseEvent(MouseReleaseEvent);
+  document->frame()->eventHandler().handleMouseReleaseEvent(mouseReleaseEvent);
 }
 
 // Makes sure that mouse hover over an custom scrollbar doesn't change the
@@ -10947,12 +10963,13 @@ TEST_F(WebFrameTest, MouseOverCustomScrollbar) {
   EXPECT_FALSE(hitTestResult.scrollbar());
 
   // Mouse over DIV
-  PlatformMouseEvent mouseMoveOverDiv(
-      IntPoint(1, 1), IntPoint(1, 1), WebPointerProperties::Button::NoButton,
-      PlatformEvent::MouseMoved, 0, PlatformEvent::NoModifiers,
-      TimeTicks::Now());
+  WebMouseEvent mouseMoveOverDiv(
+      WebInputEvent::MouseMove, WebFloatPoint(1, 1), WebFloatPoint(1, 1),
+      WebPointerProperties::Button::NoButton, 0, WebInputEvent::NoModifiers,
+      TimeTicks::Now().InSeconds());
+  mouseMoveOverDiv.setFrameScale(1);
   document->frame()->eventHandler().handleMouseMoveEvent(
-      mouseMoveOverDiv, Vector<PlatformMouseEvent>());
+      mouseMoveOverDiv, Vector<WebMouseEvent>());
 
   // DIV :hover
   EXPECT_EQ(document->hoverNode(), scrollbarDiv);
@@ -10965,12 +10982,13 @@ TEST_F(WebFrameTest, MouseOverCustomScrollbar) {
   EXPECT_TRUE(hitTestResult.scrollbar()->isCustomScrollbar());
 
   // Mouse over scrollbar
-  PlatformMouseEvent mouseMoveOverDivAndScrollbar(
-      IntPoint(175, 1), IntPoint(175, 1),
-      WebPointerProperties::Button::NoButton, PlatformEvent::MouseMoved, 0,
-      PlatformEvent::NoModifiers, TimeTicks::Now());
+  WebMouseEvent mouseMoveOverDivAndScrollbar(
+      WebInputEvent::MouseMove, WebFloatPoint(175, 1), WebFloatPoint(175, 1),
+      WebPointerProperties::Button::NoButton, 0, WebInputEvent::NoModifiers,
+      TimeTicks::Now().InSeconds());
+  mouseMoveOverDivAndScrollbar.setFrameScale(1);
   document->frame()->eventHandler().handleMouseMoveEvent(
-      mouseMoveOverDivAndScrollbar, Vector<PlatformMouseEvent>());
+      mouseMoveOverDivAndScrollbar, Vector<WebMouseEvent>());
 
   // Custom not change the DIV :hover
   EXPECT_EQ(document->hoverNode(), scrollbarDiv);
@@ -11001,41 +11019,45 @@ TEST_F(WebFrameTest, MouseReleaseUpdatesScrollbarHoveredPart) {
   EXPECT_EQ(scrollbar->hoveredPart(), ScrollbarPart::NoPart);
 
   // Mouse moved over the scrollbar.
-  PlatformMouseEvent mouseMoveOverScrollbar(
-      IntPoint(175, 1), IntPoint(175, 1),
-      WebPointerProperties::Button::NoButton, PlatformEvent::MouseMoved, 0,
-      PlatformEvent::NoModifiers, TimeTicks::Now());
+  WebMouseEvent mouseMoveOverScrollbar(
+      WebInputEvent::MouseMove, WebFloatPoint(175, 1), WebFloatPoint(175, 1),
+      WebPointerProperties::Button::NoButton, 0, WebInputEvent::NoModifiers,
+      TimeTicks::Now().InSeconds());
+  mouseMoveOverScrollbar.setFrameScale(1);
   document->frame()->eventHandler().handleMouseMoveEvent(
-      mouseMoveOverScrollbar, Vector<PlatformMouseEvent>());
+      mouseMoveOverScrollbar, Vector<WebMouseEvent>());
   HitTestResult hitTestResult = webView->coreHitTestResultAt(WebPoint(175, 1));
   EXPECT_EQ(scrollbar->pressedPart(), ScrollbarPart::NoPart);
   EXPECT_EQ(scrollbar->hoveredPart(), ScrollbarPart::ThumbPart);
 
   // Mouse pressed.
-  PlatformMouseEvent mousePressEvent(
-      IntPoint(175, 1), IntPoint(175, 1), WebPointerProperties::Button::Left,
-      PlatformEvent::MousePressed, 0, PlatformEvent::Modifiers::LeftButtonDown,
-      TimeTicks::Now());
+  WebMouseEvent mousePressEvent(
+      WebInputEvent::MouseDown, WebFloatPoint(175, 1), WebFloatPoint(175, 1),
+      WebPointerProperties::Button::Left, 0,
+      WebInputEvent::Modifiers::LeftButtonDown, TimeTicks::Now().InSeconds());
+  mousePressEvent.setFrameScale(1);
   document->frame()->eventHandler().handleMousePressEvent(mousePressEvent);
   EXPECT_EQ(scrollbar->pressedPart(), ScrollbarPart::ThumbPart);
   EXPECT_EQ(scrollbar->hoveredPart(), ScrollbarPart::ThumbPart);
 
   // Mouse moved off the scrollbar while still pressed.
-  PlatformMouseEvent mouseMoveOffScrollbar(
-      IntPoint(1, 1), IntPoint(1, 1), WebPointerProperties::Button::Left,
-      PlatformEvent::MouseMoved, 0, PlatformEvent::Modifiers::LeftButtonDown,
-      TimeTicks::Now());
+  WebMouseEvent mouseMoveOffScrollbar(
+      WebInputEvent::MouseMove, WebFloatPoint(1, 1), WebFloatPoint(1, 1),
+      WebPointerProperties::Button::Left, 0,
+      WebInputEvent::Modifiers::LeftButtonDown, TimeTicks::Now().InSeconds());
+  mouseMoveOffScrollbar.setFrameScale(1);
   document->frame()->eventHandler().handleMouseLeaveEvent(
       mouseMoveOffScrollbar);
   EXPECT_EQ(scrollbar->pressedPart(), ScrollbarPart::ThumbPart);
   EXPECT_EQ(scrollbar->hoveredPart(), ScrollbarPart::ThumbPart);
 
   // Mouse released.
-  PlatformMouseEvent MouseReleaseEvent(
-      IntPoint(1, 1), IntPoint(1, 1), WebPointerProperties::Button::Left,
-      PlatformEvent::MouseReleased, 0, PlatformEvent::Modifiers::LeftButtonDown,
-      TimeTicks::Now());
-  document->frame()->eventHandler().handleMouseReleaseEvent(MouseReleaseEvent);
+  WebMouseEvent mouseReleaseEvent(
+      WebInputEvent::MouseUp, WebFloatPoint(1, 1), WebFloatPoint(1, 1),
+      WebPointerProperties::Button::Left, 0,
+      WebInputEvent::Modifiers::LeftButtonDown, TimeTicks::Now().InSeconds());
+  mouseReleaseEvent.setFrameScale(1);
+  document->frame()->eventHandler().handleMouseReleaseEvent(mouseReleaseEvent);
   EXPECT_EQ(scrollbar->pressedPart(), ScrollbarPart::NoPart);
   EXPECT_EQ(scrollbar->hoveredPart(), ScrollbarPart::NoPart);
 }
diff --git a/third_party/WebKit/Source/web/tests/WebInputEventConversionTest.cpp b/third_party/WebKit/Source/web/tests/WebInputEventConversionTest.cpp
index 4de6fd5a38f6f9..6189e7b0e2709c 100644
--- a/third_party/WebKit/Source/web/tests/WebInputEventConversionTest.cpp
+++ b/third_party/WebKit/Source/web/tests/WebInputEventConversionTest.cpp
@@ -121,10 +121,6 @@ TEST(WebInputEventConversionTest, InputEventsScaling) {
   webViewImpl->setPageScaleFactor(2);
 
   FrameView* view = toLocalFrame(webViewImpl->page()->mainFrame())->view();
-  Document* document =
-      toLocalFrame(webViewImpl->page()->mainFrame())->document();
-  LocalDOMWindow* domWindow = document->domWindow();
-  LayoutViewItem documentLayoutView = document->layoutViewItem();
 
   {
     WebMouseEvent webMouseEvent(WebInputEvent::MouseMove,
@@ -139,13 +135,17 @@ TEST(WebInputEventConversionTest, InputEventsScaling) {
     webMouseEvent.movementX = 10;
     webMouseEvent.movementY = 10;
 
-    PlatformMouseEventBuilder platformMouseBuilder(view, webMouseEvent);
-    EXPECT_EQ(5, platformMouseBuilder.position().x());
-    EXPECT_EQ(5, platformMouseBuilder.position().y());
-    EXPECT_EQ(10, platformMouseBuilder.globalPosition().x());
-    EXPECT_EQ(10, platformMouseBuilder.globalPosition().y());
-    EXPECT_EQ(5, platformMouseBuilder.movementDelta().x());
-    EXPECT_EQ(5, platformMouseBuilder.movementDelta().y());
+    WebMouseEvent transformedEvent =
+        TransformWebMouseEvent(view, webMouseEvent);
+    IntPoint position = flooredIntPoint(transformedEvent.positionInRootFrame());
+    EXPECT_EQ(5, position.x());
+    EXPECT_EQ(5, position.y());
+    EXPECT_EQ(10, transformedEvent.globalX);
+    EXPECT_EQ(10, transformedEvent.globalY);
+
+    IntPoint movement = flooredIntPoint(transformedEvent.movementInRootFrame());
+    EXPECT_EQ(5, movement.x());
+    EXPECT_EQ(5, movement.y());
   }
 
   {
@@ -326,37 +326,6 @@ TEST(WebInputEventConversionTest, InputEventsScaling) {
     EXPECT_FLOAT_EQ(5.3f, transformedPoint.radiusX);
     EXPECT_FLOAT_EQ(5.2f, transformedPoint.radiusY);
   }
-
-  // Reverse builders should *not* go back to physical pixels, as they are used
-  // for plugins which expect CSS pixel coordinates.
-  {
-    PlatformMouseEvent platformMouseEvent(
-        IntPoint(10, 10), IntPoint(10, 10), WebPointerProperties::Button::Left,
-        PlatformEvent::MouseMoved, 1, PlatformEvent::NoModifiers,
-        PlatformMouseEvent::RealOrIndistinguishable, TimeTicks());
-    MouseEvent* mouseEvent = MouseEvent::create(
-        EventTypeNames::mousemove, domWindow, platformMouseEvent, 0, document);
-    WebMouseEventBuilder webMouseBuilder(view, documentLayoutView, *mouseEvent);
-
-    EXPECT_EQ(10, webMouseBuilder.x);
-    EXPECT_EQ(10, webMouseBuilder.y);
-    EXPECT_EQ(10, webMouseBuilder.globalX);
-    EXPECT_EQ(10, webMouseBuilder.globalY);
-    EXPECT_EQ(10, webMouseBuilder.windowX);
-    EXPECT_EQ(10, webMouseBuilder.windowY);
-  }
-
-  {
-    PlatformMouseEvent platformMouseEvent(
-        IntPoint(10, 10), IntPoint(10, 10),
-        WebPointerProperties::Button::NoButton, PlatformEvent::MouseMoved, 1,
-        PlatformEvent::NoModifiers, PlatformMouseEvent::RealOrIndistinguishable,
-        TimeTicks());
-    MouseEvent* mouseEvent = MouseEvent::create(
-        EventTypeNames::mousemove, domWindow, platformMouseEvent, 0, document);
-    WebMouseEventBuilder webMouseBuilder(view, documentLayoutView, *mouseEvent);
-    EXPECT_EQ(WebMouseEvent::Button::NoButton, webMouseBuilder.button);
-  }
 }
 
 TEST(WebInputEventConversionTest, InputEventsTransform) {
@@ -394,13 +363,18 @@ TEST(WebInputEventConversionTest, InputEventsTransform) {
     webMouseEvent.movementX = 60;
     webMouseEvent.movementY = 60;
 
-    PlatformMouseEventBuilder platformMouseBuilder(view, webMouseEvent);
-    EXPECT_EQ(30, platformMouseBuilder.position().x());
-    EXPECT_EQ(30, platformMouseBuilder.position().y());
-    EXPECT_EQ(100, platformMouseBuilder.globalPosition().x());
-    EXPECT_EQ(110, platformMouseBuilder.globalPosition().y());
-    EXPECT_EQ(20, platformMouseBuilder.movementDelta().x());
-    EXPECT_EQ(20, platformMouseBuilder.movementDelta().y());
+    WebMouseEvent transformedEvent =
+        TransformWebMouseEvent(view, webMouseEvent);
+    FloatPoint position = transformedEvent.positionInRootFrame();
+
+    EXPECT_FLOAT_EQ(30, position.x());
+    EXPECT_FLOAT_EQ(30, position.y());
+    EXPECT_EQ(100, transformedEvent.globalX);
+    EXPECT_EQ(110, transformedEvent.globalY);
+
+    IntPoint movement = flooredIntPoint(transformedEvent.movementInRootFrame());
+    EXPECT_EQ(20, movement.x());
+    EXPECT_EQ(20, movement.y());
   }
 
   {
@@ -426,23 +400,30 @@ TEST(WebInputEventConversionTest, InputEventsTransform) {
     events.push_back(&webMouseEvent1);
     events.push_back(&webMouseEvent2);
 
-    Vector<PlatformMouseEvent> coalescedevents =
-        createPlatformMouseEventVector(view, events);
+    Vector<WebMouseEvent> coalescedevents =
+        TransformWebMouseEventVector(view, events);
     EXPECT_EQ(events.size(), coalescedevents.size());
 
-    EXPECT_EQ(30, coalescedevents[0].position().x());
-    EXPECT_EQ(30, coalescedevents[0].position().y());
-    EXPECT_EQ(100, coalescedevents[0].globalPosition().x());
-    EXPECT_EQ(110, coalescedevents[0].globalPosition().y());
-    EXPECT_EQ(20, coalescedevents[0].movementDelta().x());
-    EXPECT_EQ(20, coalescedevents[0].movementDelta().y());
-
-    EXPECT_EQ(30, coalescedevents[1].position().x());
-    EXPECT_EQ(40, coalescedevents[1].position().y());
-    EXPECT_EQ(100, coalescedevents[1].globalPosition().x());
-    EXPECT_EQ(140, coalescedevents[1].globalPosition().y());
-    EXPECT_EQ(20, coalescedevents[1].movementDelta().x());
-    EXPECT_EQ(10, coalescedevents[1].movementDelta().y());
+    FloatPoint position = coalescedevents[0].positionInRootFrame();
+    EXPECT_FLOAT_EQ(30, position.x());
+    EXPECT_FLOAT_EQ(30, position.y());
+    EXPECT_EQ(100, coalescedevents[0].globalX);
+    EXPECT_EQ(110, coalescedevents[0].globalY);
+
+    IntPoint movement =
+        flooredIntPoint(coalescedevents[0].movementInRootFrame());
+    EXPECT_EQ(20, movement.x());
+    EXPECT_EQ(20, movement.y());
+
+    position = coalescedevents[1].positionInRootFrame();
+    EXPECT_FLOAT_EQ(30, position.x());
+    EXPECT_FLOAT_EQ(40, position.y());
+    EXPECT_EQ(100, coalescedevents[1].globalX);
+    EXPECT_EQ(140, coalescedevents[1].globalY);
+
+    movement = flooredIntPoint(coalescedevents[1].movementInRootFrame());
+    EXPECT_EQ(20, movement.x());
+    EXPECT_EQ(10, movement.y());
   }
 
   {
@@ -703,11 +684,14 @@ TEST(WebInputEventConversionTest, VisualViewportOffset) {
     webMouseEvent.globalX = 10;
     webMouseEvent.globalY = 10;
 
-    PlatformMouseEventBuilder platformMouseBuilder(view, webMouseEvent);
-    EXPECT_EQ(5 + visualOffset.x(), platformMouseBuilder.position().x());
-    EXPECT_EQ(5 + visualOffset.y(), platformMouseBuilder.position().y());
-    EXPECT_EQ(10, platformMouseBuilder.globalPosition().x());
-    EXPECT_EQ(10, platformMouseBuilder.globalPosition().y());
+    WebMouseEvent transformedMouseEvent =
+        TransformWebMouseEvent(view, webMouseEvent);
+    IntPoint position =
+        flooredIntPoint(transformedMouseEvent.positionInRootFrame());
+    EXPECT_EQ(5 + visualOffset.x(), position.x());
+    EXPECT_EQ(5 + visualOffset.y(), position.y());
+    EXPECT_EQ(10, transformedMouseEvent.globalX);
+    EXPECT_EQ(10, transformedMouseEvent.globalY);
   }
 
   {
@@ -811,13 +795,15 @@ TEST(WebInputEventConversionTest, ElasticOverscroll) {
     webMouseEvent.globalX = 10;
     webMouseEvent.globalY = 50;
 
-    PlatformMouseEventBuilder platformMouseBuilder(view, webMouseEvent);
-    EXPECT_EQ(webMouseEvent.x + elasticOverscroll.width(),
-              platformMouseBuilder.position().x());
-    EXPECT_EQ(webMouseEvent.y + elasticOverscroll.height(),
-              platformMouseBuilder.position().y());
-    EXPECT_EQ(webMouseEvent.globalX, platformMouseBuilder.globalPosition().x());
-    EXPECT_EQ(webMouseEvent.globalY, platformMouseBuilder.globalPosition().y());
+    WebMouseEvent transformedMouseEvent =
+        TransformWebMouseEvent(view, webMouseEvent);
+    IntPoint position =
+        flooredIntPoint(transformedMouseEvent.positionInRootFrame());
+
+    EXPECT_EQ(webMouseEvent.x + elasticOverscroll.width(), position.x());
+    EXPECT_EQ(webMouseEvent.y + elasticOverscroll.height(), position.y());
+    EXPECT_EQ(webMouseEvent.globalX, transformedMouseEvent.globalX);
+    EXPECT_EQ(webMouseEvent.globalY, transformedMouseEvent.globalY);
   }
 
   // Elastic overscroll and pinch-zoom (this doesn't actually ever happen,
@@ -838,15 +824,19 @@ TEST(WebInputEventConversionTest, ElasticOverscroll) {
     webMouseEvent.globalX = 10;
     webMouseEvent.globalY = 10;
 
-    PlatformMouseEventBuilder platformMouseBuilder(view, webMouseEvent);
+    WebMouseEvent transformedMouseEvent =
+        TransformWebMouseEvent(view, webMouseEvent);
+    IntPoint position =
+        flooredIntPoint(transformedMouseEvent.positionInRootFrame());
+
     EXPECT_EQ(webMouseEvent.x / pageScale + visualOffset.x() +
                   elasticOverscroll.width(),
-              platformMouseBuilder.position().x());
+              position.x());
     EXPECT_EQ(webMouseEvent.y / pageScale + visualOffset.y() +
                   elasticOverscroll.height(),
-              platformMouseBuilder.position().y());
-    EXPECT_EQ(webMouseEvent.globalX, platformMouseBuilder.globalPosition().x());
-    EXPECT_EQ(webMouseEvent.globalY, platformMouseBuilder.globalPosition().y());
+              position.y());
+    EXPECT_EQ(webMouseEvent.globalX, transformedMouseEvent.globalX);
+    EXPECT_EQ(webMouseEvent.globalY, transformedMouseEvent.globalY);
   }
 }
 
@@ -884,13 +874,15 @@ TEST(WebInputEventConversionTest, ElasticOverscrollWithPageReload) {
     webMouseEvent.globalX = 10;
     webMouseEvent.globalY = 50;
 
-    PlatformMouseEventBuilder platformMouseBuilder(view, webMouseEvent);
-    EXPECT_EQ(webMouseEvent.x + elasticOverscroll.width(),
-              platformMouseBuilder.position().x());
-    EXPECT_EQ(webMouseEvent.y + elasticOverscroll.height(),
-              platformMouseBuilder.position().y());
-    EXPECT_EQ(webMouseEvent.globalX, platformMouseBuilder.globalPosition().x());
-    EXPECT_EQ(webMouseEvent.globalY, platformMouseBuilder.globalPosition().y());
+    WebMouseEvent transformedMouseEvent =
+        TransformWebMouseEvent(view, webMouseEvent);
+    IntPoint position =
+        flooredIntPoint(transformedMouseEvent.positionInRootFrame());
+
+    EXPECT_EQ(webMouseEvent.x + elasticOverscroll.width(), position.x());
+    EXPECT_EQ(webMouseEvent.y + elasticOverscroll.height(), position.y());
+    EXPECT_EQ(webMouseEvent.globalX, transformedMouseEvent.globalX);
+    EXPECT_EQ(webMouseEvent.globalY, transformedMouseEvent.globalY);
   }
 }
 
diff --git a/third_party/WebKit/public/platform/WebInputEvent.h b/third_party/WebKit/public/platform/WebInputEvent.h
index 99e27f0810b4b9..9efd6a8781a376 100644
--- a/third_party/WebKit/public/platform/WebInputEvent.h
+++ b/third_party/WebKit/public/platform/WebInputEvent.h
@@ -187,6 +187,11 @@ class WebInputEvent {
 
     ScrollLockOn = 1 << 18,
 
+    // Whether this is a compatibility event generated due to a
+    // native touch event. Mouse events generated from touch
+    // events will set this.
+    IsCompatibilityEventForTouch = 1 << 19,
+
     // The set of non-stateful modifiers that specifically change the
     // interpretation of the key being pressed. For example; IsLeft,
     // IsRight, IsComposing don't change the meaning of the key
diff --git a/third_party/WebKit/public/platform/WebMouseEvent.h b/third_party/WebKit/public/platform/WebMouseEvent.h
index ec23a72f442ff2..c9e5a419d1edf8 100644
--- a/third_party/WebKit/public/platform/WebMouseEvent.h
+++ b/third_party/WebKit/public/platform/WebMouseEvent.h
@@ -9,6 +9,8 @@
 
 namespace blink {
 
+class WebGestureEvent;
+
 // See WebInputEvent.h for details why this pack is here.
 #pragma pack(push, 4)
 
@@ -34,16 +36,69 @@ class WebMouseEvent : public WebInputEvent, public WebPointerProperties {
   int movementY;
   int clickCount;
 
-  WebMouseEvent(Type type, int modifiers, double timeStampSeconds)
-      : WebInputEvent(sizeof(WebMouseEvent), type, modifiers, timeStampSeconds),
-        WebPointerProperties() {}
-
-  WebMouseEvent()
-      : WebInputEvent(sizeof(WebMouseEvent)), WebPointerProperties() {}
+  WebMouseEvent(Type typeParam,
+                int xParam,
+                int yParam,
+                int globalXParam,
+                int globalYParam,
+                int modifiersParam,
+                double timeStampSecondsParam)
+      : WebInputEvent(sizeof(WebMouseEvent),
+                      typeParam,
+                      modifiersParam,
+                      timeStampSecondsParam),
+        WebPointerProperties(),
+        x(xParam),
+        y(yParam),
+        globalX(globalXParam),
+        globalY(globalYParam) {}
+
+  WebMouseEvent(Type typeParam,
+                WebFloatPoint position,
+                WebFloatPoint globalPosition,
+                Button buttonParam,
+                int clickCountParam,
+                int modifiersParam,
+                double timeStampSecondsParam)
+      : WebInputEvent(sizeof(WebMouseEvent),
+                      typeParam,
+                      modifiersParam,
+                      timeStampSecondsParam),
+        WebPointerProperties(buttonParam, PointerType::Mouse),
+        x(position.x),
+        y(position.y),
+        globalX(globalPosition.x),
+        globalY(globalPosition.y),
+        clickCount(clickCountParam) {}
+
+  WebMouseEvent(Type typeParam,
+                int modifiersParam,
+                double timeStampSecondsParam)
+      : WebMouseEvent(sizeof(WebMouseEvent),
+                      typeParam,
+                      modifiersParam,
+                      timeStampSecondsParam) {}
+
+  WebMouseEvent() : WebMouseEvent(sizeof(WebMouseEvent)) {}
+
+  bool fromTouch() const {
+    return (modifiers() & IsCompatibilityEventForTouch) != 0;
+  }
 
 #if INSIDE_BLINK
+  BLINK_PLATFORM_EXPORT WebMouseEvent(Type typeParam,
+                                      const WebGestureEvent&,
+                                      Button buttonParam,
+                                      int clickCountParam,
+                                      int modifiersParam,
+                                      double timeStampSecondsParam);
+
   BLINK_PLATFORM_EXPORT WebFloatPoint movementInRootFrame() const;
   BLINK_PLATFORM_EXPORT WebFloatPoint positionInRootFrame() const;
+
+  // Sets any scaled values to be their computed values and sets |frameScale|
+  // back to 1 and |translateX|, |translateY| back to 0.
+  BLINK_PLATFORM_EXPORT WebMouseEvent flattenTransform() const;
 #endif
 
  protected:
diff --git a/third_party/WebKit/public/platform/WebPointerProperties.h b/third_party/WebKit/public/platform/WebPointerProperties.h
index 86f2960081b822..27e59c44268912 100644
--- a/third_party/WebKit/public/platform/WebPointerProperties.h
+++ b/third_party/WebKit/public/platform/WebPointerProperties.h
@@ -17,16 +17,6 @@ namespace blink {
 // WebTouchEvent and WebTouchPoint and merge this into WebPointerEvent.
 class WebPointerProperties {
  public:
-  WebPointerProperties()
-      : id(0),
-        force(std::numeric_limits<float>::quiet_NaN()),
-        tiltX(0),
-        tiltY(0),
-        tangentialPressure(0.0f),
-        twist(0),
-        button(Button::NoButton),
-        pointerType(PointerType::Unknown) {}
-
   enum class Button { NoButton = -1, Left, Middle, Right, X1, X2, Eraser };
 
   enum class Buttons : unsigned {
@@ -48,6 +38,26 @@ class WebPointerProperties {
     LastEntry = Touch  // Must be the last entry in the list
   };
 
+  WebPointerProperties()
+      : id(0),
+        force(std::numeric_limits<float>::quiet_NaN()),
+        tiltX(0),
+        tiltY(0),
+        tangentialPressure(0.0f),
+        twist(0),
+        button(Button::NoButton),
+        pointerType(PointerType::Unknown) {}
+
+  WebPointerProperties(Button buttonParam, PointerType pointerTypeParam)
+      : id(0),
+        force(std::numeric_limits<float>::quiet_NaN()),
+        tiltX(0),
+        tiltY(0),
+        tangentialPressure(0.0f),
+        twist(0),
+        button(buttonParam),
+        pointerType(pointerTypeParam) {}
+
   int id;
 
   // The valid range is [0,1], with NaN meaning pressure is not supported by