Fixed bug that caused canvas updates to trigger two compositor paints.

content/renderer/render_widget.h

Index: content/renderer/render_widget.h
diff --git a/content/renderer/render_widget.h b/content/renderer/render_widget.h
index e6c896f8ad904d541d9e012f3f69fc583f8601d7..fa55acb0c60e2df1cd42807e0928b6bb52134a08 100644
--- a/content/renderer/render_widget.h
+++ b/content/renderer/render_widget.h
@@ -102,6 +102,7 @@ class RenderWidget : public IPC::Channel::Listener,
   virtual void didActivateAcceleratedCompositing(bool active);
   virtual void scheduleComposite();
   virtual void scheduleAnimation();
+  virtual void popPendingUpdate();
   virtual void didFocus();
   virtual void didBlur();
   virtual void didChangeCursor(const WebKit::WebCursorInfo&);
@@ -334,6 +335,7 @@ class RenderWidget : public IPC::Channel::Listener,
   TransportDIB* current_paint_buf_;
 
   PaintAggregator paint_aggregator_;
+  PaintAggregator::PendingUpdate paint_aggregator_update_;
 
   // The area that must be reserved for drawing the resize corner.
   gfx::Rect resizer_rect_;