Detect wheel zoom via WheelPrefs instead of the Ctrl modifier. (bug 1…

…127700, r=smaug)

dom/events/EventStateManager.cpp

@@ -5489,6 +5489,12 @@ EventStateManager::WheelPrefs::NeedToComputeLineOrPageDelta(
          (mMultiplierY[index] != 1.0 && mMultiplierY[index] != -1.0);
 }
 
+bool
+EventStateManager::WheelEventIsScrollAction(WidgetWheelEvent* aEvent)
+{
+  return WheelPrefs::GetInstance()->ComputeActionFor(aEvent) == WheelPrefs::ACTION_SCROLL;
+}
+
 bool
 EventStateManager::WheelPrefs::IsOverOnePageScrollAllowedX(
                                  WidgetWheelEvent* aEvent)

dom/events/EventStateManager.h

@@ -224,6 +224,9 @@ class EventStateManager : public nsSupportsWeakReference,
   static LayoutDeviceIntPoint GetChildProcessOffset(nsFrameLoader* aFrameLoader,
                                                     const WidgetEvent& aEvent);
 
+  // Returns true if the given WidgetWheelEvent will resolve to a scroll action.
+  static bool WheelEventIsScrollAction(WidgetWheelEvent* aEvent);
+
   // Holds the point in screen coords that a mouse event was dispatched to,
   // before we went into pointer lock mode. This is constantly updated while
   // the pointer is not locked, but we don't update it while the pointer is

gfx/layers/apz/src/APZCTreeManager.cpp

@@ -19,6 +19,7 @@
 #include "mozilla/mozalloc.h"           // for operator new
 #include "mozilla/TouchEvents.h"
 #include "mozilla/Preferences.h"        // for Preferences
+#include "mozilla/EventStateManager.h"  // for WheelPrefs
 #include "nsDebug.h"                    // for NS_WARNING
 #include "nsPoint.h"                    // for nsIntPoint
 #include "nsThreadUtils.h"              // for NS_IsMainThread
@@ -891,11 +892,11 @@ APZCTreeManager::ReceiveInputEvent(WidgetInputEvent& aEvent,
     }
     case eWheelEventClass: {
       WidgetWheelEvent& wheelEvent = *aEvent.AsWheelEvent();
-      if (wheelEvent.IsControl() ||
-          wheelEvent.deltaMode != nsIDOMWheelEvent::DOM_DELTA_LINE)
+      if (wheelEvent.deltaMode != nsIDOMWheelEvent::DOM_DELTA_LINE ||
+          !EventStateManager::WheelEventIsScrollAction(&wheelEvent))
       {
-        // Don't send through APZ if we could be ctrl+zooming or if the delta
-        // mode is not line-based.
+        // Don't send through APZ if we're not scrolling or if the delta mode
+        // is not line-based.
         return ProcessEvent(aEvent, aOutTargetGuid, aOutInputBlockId);
       }
       return ProcessWheelEvent(wheelEvent, aOutTargetGuid, aOutInputBlockId);