Make RenderWidgetHostViewAura::CopyFromCompositingSurface readback layer

content/browser/renderer_host/render_widget_host_view_base.h

Index: content/browser/renderer_host/render_widget_host_view_base.h
diff --git a/content/browser/renderer_host/render_widget_host_view_base.h b/content/browser/renderer_host/render_widget_host_view_base.h
index 37e47fc876350ecde01837411b1417ac5db91203..14aeb6d2429d8995b227f0eadd7da7c25252bc07 100644
--- a/content/browser/renderer_host/render_widget_host_view_base.h
+++ b/content/browser/renderer_host/render_widget_host_view_base.h
@@ -79,12 +79,16 @@ class CONTENT_EXPORT RenderWidgetHostViewBase
       scoped_ptr<cc::CompositorFrame> frame) OVERRIDE {}
   virtual void OnOverscrolled(gfx::Vector2dF accumulated_overscroll,
                               gfx::Vector2dF current_fling_velocity) OVERRIDE;
+  virtual uint32 RendererFrameNumber() OVERRIDE;
 
   void SetBrowserAccessibilityManager(BrowserAccessibilityManager* manager);
 
   // Notification that a resize or move session ended on the native widget.
   void UpdateScreenInfo(gfx::NativeView view);
 
+  // Subclasses should call this when they receieve a frame from the renderer.
+  void DidReceiveRendererFrame();
+
 #if defined(OS_WIN)
   // The callback that DetachPluginsHelper calls for each child window. Call
   // this directly if you want to do custom filtering on plugin windows first.
@@ -148,6 +152,8 @@ protected:
 
   gfx::Rect current_display_area_;
 
+  uint32 renderer_frame_number_;
+
   DISALLOW_COPY_AND_ASSIGN(RenderWidgetHostViewBase);
 };