Add a WebContentsImpl API to snapshot the accessibility tree.

content/browser/frame_host/render_frame_host_impl.h

Index: content/browser/frame_host/render_frame_host_impl.h
diff --git a/content/browser/frame_host/render_frame_host_impl.h b/content/browser/frame_host/render_frame_host_impl.h
index 67ee5d52858553fc8608c7bb5691aa1006b2411d..7c1c49a30f0f94bf5af3aff0a184fd70850a8bb0 100644
--- a/content/browser/frame_host/render_frame_host_impl.h
+++ b/content/browser/frame_host/render_frame_host_impl.h
@@ -365,6 +365,12 @@ class CONTENT_EXPORT RenderFrameHostImpl
   // Send a message to the renderer process to change the accessibility mode.
   void SetAccessibilityMode(AccessibilityMode AccessibilityMode);
 
+  // Request a one-time snapshot of the accessibility tree without changing
+  // the accessibility mode.
+  typedef base::Callback<void(const ui::AXTreeUpdate&)>

[Charlie Reis, 2015/04/02 23:09:06]

Style nit: typedefs belong at the top.
http://google-styleguide.googlecode.com/svn/trunk/cppguide.html#Declaration_O...

[dmazzoni, 2015/04/03 22:49:42]

Done.

+      AXTreeSnapshotCallback;
+  void RequestAXTreeSnapshot(AXTreeSnapshotCallback callback);
+
   // Turn on accessibility testing. The given callback will be run
   // every time an accessibility notification is received from the
   // renderer process, and the accessibility tree it sent can be
@@ -507,6 +513,8 @@ class CONTENT_EXPORT RenderFrameHostImpl
       const std::vector<AccessibilityHostMsg_LocationChangeParams>& params);
   void OnAccessibilityFindInPageResult(
       const AccessibilityHostMsg_FindInPageResultParams& params);
+  void OnAccessibilitySnapshotResponse(int token,
+                                       const ui::AXTreeUpdate& snapshot);
   void OnToggleFullscreen(bool enter_fullscreen);
 
 #if defined(OS_MACOSX) || defined(OS_ANDROID)
@@ -677,6 +685,10 @@ class CONTENT_EXPORT RenderFrameHostImpl
   // we don't keep trying to reset forever.
   int accessibility_reset_count_;
 
+  // The mapping of pending accessibility tree snapshot calls created by
+  // RequestAXTreeSnapshot and their corresponding callbacks.

[Charlie Reis, 2015/04/02 23:09:06]

Please say what the key is.

[dmazzoni, 2015/04/03 22:49:42]

Reworded. If this wording looks better, I can modify the same map used for
ExecuteJavaScript, above.

+  std::map<int, AXTreeSnapshotCallback> ax_tree_snapshot_callbacks_;
+
   // Callback when an event is received, for testing.
   base::Callback<void(ui::AXEvent, int)> accessibility_testing_callback_;
   // The most recently received accessibility tree - for testing only.