Cross-process iframe accessibility.

This change completes the plumbing to join cross-process iframes into a single composed accessibility tree on platforms that implement native accessibility APIs (Windows, Mac, Android).

Further work will be needed to update some accessibility API implementations to be multi-frame-aware.

BUG=368298

Review URL: https://codereview.chromium.org/268543008

Cr-Commit-Position: refs/heads/master@{#294118}

content/browser/accessibility/accessibility_tree_formatter.cc

@@ -66,7 +66,7 @@ void AccessibilityTreeFormatter::RecursiveBuildAccessibilityTree(
   dict->Set(kChildrenDictAttr, children);
 
   for (size_t i = 0; i < node.PlatformChildCount(); ++i) {
-    BrowserAccessibility* child_node = node.InternalGetChild(i);
+    BrowserAccessibility* child_node = node.PlatformGetChild(i);
     base::DictionaryValue* child_dict = new base::DictionaryValue;
     children->Append(child_dict);
     RecursiveBuildAccessibilityTree(*child_node, child_dict);

content/browser/accessibility/browser_accessibility.cc

@@ -26,7 +26,8 @@ BrowserAccessibility* BrowserAccessibility::Create() {
 
 BrowserAccessibility::BrowserAccessibility()
     : manager_(NULL),
-      node_(NULL) {
+      node_(NULL),
+      child_frame_tree_node_id_(0) {
 }
 
 BrowserAccessibility::~BrowserAccessibility() {
@@ -63,6 +64,15 @@ bool BrowserAccessibility::PlatformIsLeaf() const {
 }
 
 uint32 BrowserAccessibility::PlatformChildCount() const {
+  if (child_frame_tree_node_id_ &&
+      manager_ && manager_->delegate()) {
+    BrowserAccessibilityManager* child_manager =
+        manager_->delegate()->AccessibilityGetChildFrame(
+            child_frame_tree_node_id_);
+    if (child_manager)
+      return 1;
+  }
+
   return PlatformIsLeaf() ? 0 : InternalChildCount();
 }
 
@@ -83,6 +93,16 @@ bool BrowserAccessibility::IsDescendantOf(
 
 BrowserAccessibility* BrowserAccessibility::PlatformGetChild(
     uint32 child_index) const {
+  if (child_index == 0 && child_frame_tree_node_id_ &&
+      manager_ &&
+      manager_->delegate()) {
+    BrowserAccessibilityManager* child_manager =
+        manager_->delegate()->AccessibilityGetChildFrame(
+            child_frame_tree_node_id_);
+    if (child_manager)
+      return child_manager->GetRoot();
+  }
+
   DCHECK(child_index < InternalChildCount());
   return InternalGetChild(child_index);
 }
@@ -122,7 +142,9 @@ BrowserAccessibility* BrowserAccessibility::GetParent() const {
   if (!node_ || !manager_)
     return NULL;
   ui::AXNode* parent = node_->parent();
-  return parent ? manager_->GetFromAXNode(parent) : NULL;
+  if (parent)
+    return manager_->GetFromAXNode(parent);
+  return manager_->GetCrossFrameParent();
 }
 
 int32 BrowserAccessibility::GetIndexInParent() const {
@@ -680,4 +702,10 @@ int BrowserAccessibility::GetStaticTextLenRecursive() const {
   return len;
 }
 
+void BrowserAccessibility::SetChildFrameTreeNodeId(
+    int64 child_frame_tree_node_id) {
+  child_frame_tree_node_id_ = child_frame_tree_node_id;
+  manager_->NotifyAccessibilityEvent(ui::AX_EVENT_CHILDREN_CHANGED, this);
+}
+
 }  // namespace content

content/browser/accessibility/browser_accessibility.h

@@ -31,12 +31,13 @@ class BrowserAccessibilityWin;
 //
 // BrowserAccessibility
 //
-// Class implementing the cross platform interface for the Browser-Renderer
-// communication of accessibility information, providing accessibility
-// to be used by screen readers and other assistive technology (AT).
+// A BrowserAccessibility object represents one node in the accessibility
+// tree on the browser side. It exactly corresponds to one WebAXObject from
+// Blink. It's owned by a BrowserAccessibilityManager.
 //
-// An implementation for each platform handles platform specific accessibility
-// APIs.
+// There are subclasses of BrowserAccessibility for each platform where
+// we implement native accessibility APIs. This base class is used occasionally
+// for tests.
 //
 ////////////////////////////////////////////////////////////////////////////////
 class CONTENT_EXPORT BrowserAccessibility {
@@ -245,6 +246,15 @@ class CONTENT_EXPORT BrowserAccessibility {
   // Append the text from this node and its children.
   std::string GetTextRecursive() const;
 
+  // Identifies the given frame tree node id as the only child of this node,
+  // so any call to PlatformChildCount/PlatformGetChild will use
+  // BrowserAccessibilityDelegate::AccessibilityGetChildFrame to retrieve
+  // the BrowserAccessibilityManager of the child frame and return its root
+  // node as this node's child.
+  void SetChildFrameTreeNodeId(int64 child_frame_tree_node_id);
+
+  int64 child_frame_tree_node_id() const { return child_frame_tree_node_id_; }
+
  protected:
   BrowserAccessibility();
 
@@ -262,7 +272,9 @@ class CONTENT_EXPORT BrowserAccessibility {
   std::string name_;
   std::string value_;
 
- private:
+  // If nonzero, the frame tree node id of the child frame of this node.
+  int64 child_frame_tree_node_id_;
+
   DISALLOW_COPY_AND_ASSIGN(BrowserAccessibility);
 };
 

content/browser/accessibility/browser_accessibility_manager.cc

@@ -7,9 +7,38 @@
 #include "base/logging.h"
 #include "content/browser/accessibility/browser_accessibility.h"
 #include "content/common/accessibility_messages.h"
+#include "ui/accessibility/ax_tree_serializer.h"
 
 namespace content {
 
+namespace {
+
+// Recursively searches |ancestor_node| and its descendants for a
+// BrowserAccessibility with |child| as its immediate and only child.
+// Searches only the frame that |ancestor_node| belongs to, does not descend
+// into child frames (but |child| can be the root of another frame).
+BrowserAccessibility* FindParentOfNode(
+    BrowserAccessibility* ancestor_node, BrowserAccessibility* child) {
+  if (ancestor_node->PlatformChildCount() == 1 &&
+      ancestor_node->PlatformGetChild(0) == child) {
+    return ancestor_node;
+  }
+
+  if (ancestor_node->InternalChildCount() == 0)
+    return NULL;
+
+  for (uint32 i = 0; i < ancestor_node->PlatformChildCount(); ++i) {
+    BrowserAccessibility* result = FindParentOfNode(
+        ancestor_node->PlatformGetChild(i), child);
+    if (result)
+      return result;
+  }
+
+  return NULL;
+}
+
+}  // namespace.
+
 ui::AXTreeUpdate MakeAXTreeUpdate(
     const ui::AXNodeData& node1,
     const ui::AXNodeData& node2 /* = ui::AXNodeData() */,
@@ -67,7 +96,7 @@ BrowserAccessibilityManager::BrowserAccessibilityManager(
     BrowserAccessibilityFactory* factory)
     : delegate_(delegate),
       factory_(factory),
-      tree_(new ui::AXTree()),
+      tree_(new ui::AXSerializableTree()),
       focus_(NULL),
       osk_state_(OSK_ALLOWED) {
   tree_->SetDelegate(this);
@@ -79,7 +108,7 @@ BrowserAccessibilityManager::BrowserAccessibilityManager(
     BrowserAccessibilityFactory* factory)
     : delegate_(delegate),
       factory_(factory),
-      tree_(new ui::AXTree()),
+      tree_(new ui::AXSerializableTree()),
       focus_(NULL),
       osk_state_(OSK_ALLOWED) {
   tree_->SetDelegate(this);
@@ -363,4 +392,40 @@ void BrowserAccessibilityManager::OnNodeChangeFinished(ui::AXNode* node) {
   GetFromAXNode(node)->OnUpdateFinished();
 }
 
+ui::AXTreeUpdate BrowserAccessibilityManager::SnapshotAXTreeForTesting() {
+  scoped_ptr<ui::AXTreeSource<const ui::AXNode*> > tree_source(
+      tree_->CreateTreeSource());
+  ui::AXTreeSerializer<const ui::AXNode*> serializer(tree_source.get());
+  ui::AXTreeUpdate update;
+  serializer.SerializeChanges(tree_->GetRoot(), &update);
+  return update;
+}
+
+void BrowserAccessibilityManager::SetChildFrameTreeNodeId(
+    int32 node_id, int64 child_frame_tree_node_id) {
+  BrowserAccessibility* node = GetFromID(node_id);
+  if (node) {
+    // The node id passed to us is the web area for the proxy frame.
+    // In order to replace this node with the child frame, set the
+    // child frame id on its parent.
+    BrowserAccessibility* node_parent = node->GetParent();
+    if (node_parent)
+      node_parent->SetChildFrameTreeNodeId(child_frame_tree_node_id);
+  }
+}
+
+BrowserAccessibility* BrowserAccessibilityManager::GetCrossFrameParent() {
+  if (!delegate_)
+    return NULL;
+
+  BrowserAccessibilityManager* parent_frame =
+      delegate_->AccessibilityGetParentFrame();
+  if (!parent_frame)
+    return NULL;
+
+  // Recursively search the parent frame to find the node that has this
+  // frame as its child.
+  return FindParentOfNode(parent_frame->GetRoot(), GetRoot());
+}
+
 }  // namespace content

content/browser/accessibility/browser_accessibility_manager.h

@@ -13,7 +13,7 @@
 #include "content/common/content_export.h"
 #include "third_party/WebKit/public/web/WebAXEnums.h"
 #include "ui/accessibility/ax_node_data.h"
-#include "ui/accessibility/ax_tree.h"
+#include "ui/accessibility/ax_serializable_tree.h"
 #include "ui/accessibility/ax_tree_update.h"
 #include "ui/gfx/native_widget_types.h"
 
@@ -22,6 +22,7 @@ struct AccessibilityHostMsg_LocationChangeParams;
 
 namespace content {
 class BrowserAccessibility;
+class BrowserAccessibilityManager;
 #if defined(OS_ANDROID)
 class BrowserAccessibilityManagerAndroid;
 #endif
@@ -42,6 +43,12 @@ CONTENT_EXPORT ui::AXTreeUpdate MakeAXTreeUpdate(
     const ui::AXNodeData& node9 = ui::AXNodeData());
 
 // Class that can perform actions on behalf of the BrowserAccessibilityManager.
+// Note: BrowserAccessibilityManager should never cache any of the return
+// values from any of these interfaces, especially those that return pointers.
+// They may only be valid within this call stack. That policy eliminates any
+// concerns about ownership and lifecycle issues; none of these interfaces
+// transfer ownership and no return values are guaranteed to be valid outside
+// of the current call stack.
 class CONTENT_EXPORT BrowserAccessibilityDelegate {
  public:
   virtual ~BrowserAccessibilityDelegate() {}
@@ -63,6 +70,9 @@ class CONTENT_EXPORT BrowserAccessibilityDelegate {
   virtual void AccessibilityFatalError() = 0;
   virtual gfx::AcceleratedWidget AccessibilityGetAcceleratedWidget() = 0;
   virtual gfx::NativeViewAccessible AccessibilityGetNativeViewAccessible() = 0;
+  virtual BrowserAccessibilityManager* AccessibilityGetChildFrame(
+      int64 frame_tree_node_id) = 0;
+  virtual BrowserAccessibilityManager* AccessibilityGetParentFrame() = 0;
 };
 
 class CONTENT_EXPORT BrowserAccessibilityFactory {
@@ -189,6 +199,13 @@ class CONTENT_EXPORT BrowserAccessibilityManager : public ui::AXTreeDelegate {
     delegate_ = delegate;
   }
 
+  // Get a snapshot of the current tree as an AXTreeUpdate.
+  ui::AXTreeUpdate SnapshotAXTreeForTesting();
+
+  // Frame tree support.
+  void SetChildFrameTreeNodeId(int32 node_id, int64 child_frame_tree_node_id);
+  BrowserAccessibility* GetCrossFrameParent();
+
  protected:
   BrowserAccessibilityManager(
       BrowserAccessibilityDelegate* delegate,
@@ -225,21 +242,6 @@ class CONTENT_EXPORT BrowserAccessibilityManager : public ui::AXTreeDelegate {
     OSK_ALLOWED
   };
 
-  // Update a set of nodes using data received from the renderer
-  // process.
-  bool UpdateNodes(const std::vector<ui::AXNodeData>& nodes);
-
-  // Update one node from the tree using data received from the renderer
-  // process. Returns true on success, false on fatal error.
-  bool UpdateNode(const ui::AXNodeData& src);
-
-  void SetRoot(BrowserAccessibility* root);
-
-  BrowserAccessibility* CreateNode(
-      BrowserAccessibility* parent,
-      int32 id,
-      int32 index_in_parent);
-
  protected:
   // The object that can perform actions on our behalf.
   BrowserAccessibilityDelegate* delegate_;
@@ -248,7 +250,7 @@ class CONTENT_EXPORT BrowserAccessibilityManager : public ui::AXTreeDelegate {
   scoped_ptr<BrowserAccessibilityFactory> factory_;
 
   // The underlying tree of accessibility objects.
-  scoped_ptr<ui::AXTree> tree_;
+  scoped_ptr<ui::AXSerializableTree> tree_;
 
   // The node that currently has focus.
   ui::AXNode* focus_;

content/browser/accessibility/browser_accessibility_manager_unittest.cc

@@ -97,6 +97,13 @@ class TestBrowserAccessibilityDelegate
       OVERRIDE {
     return NULL;
   }
+  virtual BrowserAccessibilityManager* AccessibilityGetChildFrame(
+      int64 frame_tree_node_id) OVERRIDE {
+    return NULL;
+  }
+  virtual BrowserAccessibilityManager* AccessibilityGetParentFrame() OVERRIDE {
+    return NULL;
+  }
 
   bool got_fatal_error() const { return got_fatal_error_; }
   void reset_got_fatal_error() { got_fatal_error_ = false; }