Make RenderWidgetHostViewAura::CopyFromCompositingSurface readback layer

content/port/browser/render_widget_host_view_port.h

Index: content/port/browser/render_widget_host_view_port.h
diff --git a/content/port/browser/render_widget_host_view_port.h b/content/port/browser/render_widget_host_view_port.h
index 9b1f7fc10b00f8ba30d4762eafbbcf00626f2292..74e2e97a55a93d2c1dcd7a8a5a2b30bca48102d6 100644
--- a/content/port/browser/render_widget_host_view_port.h
+++ b/content/port/browser/render_widget_host_view_port.h
@@ -295,6 +295,10 @@ class CONTENT_EXPORT RenderWidgetHostViewPort : public RenderWidgetHostView,
   virtual void OnAccessibilityNotifications(
       const std::vector<AccessibilityHostMsg_NotificationParams>& params) = 0;
 
+  // Return a value that is incremented each time the renderer swaps a new frame
+  // to the view.
+  virtual uint32 RendererFrameNumber() = 0;
+
 #if defined(OS_MACOSX)
   // Called just before GetBackingStore blocks for an updated frame.
   virtual void AboutToWaitForBackingStoreMsg() = 0;