Implement initial support for nesting one ax tree in another.

content/browser/accessibility/browser_accessibility_manager.h

Index: content/browser/accessibility/browser_accessibility_manager.h
diff --git a/content/browser/accessibility/browser_accessibility_manager.h b/content/browser/accessibility/browser_accessibility_manager.h
index 932a435bd7adb9168fa2fc5e8379118afbd50ebb..c4e1d96cd29ce58b39b2ace64f1636f1d563af51 100644
--- a/content/browser/accessibility/browser_accessibility_manager.h
+++ b/content/browser/accessibility/browser_accessibility_manager.h
@@ -178,6 +178,11 @@ class CONTENT_EXPORT BrowserAccessibilityManager : public ui::AXTreeDelegate {
 
   BrowserAccessibilityDelegate* delegate() const { return delegate_; }
 
+  // Frame tree support.
+  void SetParentFrameIds(uint32 parent_frame_frame_id,
+                         uint32 parent_frame_node_id);
+  BrowserAccessibility* GetCrossFrameParent();
+
  protected:
   BrowserAccessibilityManager(
       BrowserAccessibilityDelegate* delegate,
@@ -242,6 +247,17 @@ class CONTENT_EXPORT BrowserAccessibilityManager : public ui::AXTreeDelegate {
   // A mapping from a node id to its wrapper of type BrowserAccessibility.
   base::hash_map<int32, BrowserAccessibility*> id_wrapper_map_;
 
+  // This and the following field are set if this tree's frame is the child
+  // of another frame.
+  //
+  // The id of the parent frame, which can be mapped to another
+  // BrowserAccessibilityManager using FrameTreeAccessibility.
+  uint32 parent_frame_frame_id_;

[aboxhall, 2014/05/06 15:41:27]

I'm wondering whether this and the below should be a struct. Possibly not, just
an idea.

+
+  // If |parent_frame_frame_id_| is not kNoFrameId, then this is the
+  // id of the hosting node within the parent frame.
+  uint32 parent_frame_node_id_;
+
   // The on-screen keyboard state.
   OnScreenKeyboardState osk_state_;