Skip screen update when the WebView isn't ready to paint.

chrome/renderer/render_widget.h

Index: chrome/renderer/render_widget.h
diff --git a/chrome/renderer/render_widget.h b/chrome/renderer/render_widget.h
index 7f9e24790a40bb9fcd9027204e364a0228eafdee..8de40ccb027c35bad20b01c071421faee8a9893f 100644
--- a/chrome/renderer/render_widget.h
+++ b/chrome/renderer/render_widget.h
@@ -241,6 +241,10 @@ class RenderWidget : public IPC::Channel::Listener,
   // just handled.
   virtual void DidHandleMouseEvent(const WebKit::WebMouseEvent& event) {}
 
+  // Used to determine wheter does DoDeferredUpdate()
+  // The web page might not be loaded enough to paint.
+  virtual bool IsReadyToPaint() const { return true; }
+
   // Routing ID that allows us to communicate to the parent browser process
   // RenderWidgetHost. When MSG_ROUTING_NONE, no messages may be sent.
   int32 routing_id_;