Avoid sending empty OnRepaint msgs and propagate window damage correctly

content/renderer/render_widget.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_RENDERER_RENDER_WIDGET_H_
 #define CONTENT_RENDERER_RENDER_WIDGET_H_
 
 #include <deque>
 #include <map>
 
@@ skipping 290 matching lines @@
       const string16& text,
       const std::vector<WebKit::WebCompositionUnderline>& underlines,
       int selection_start,
       int selection_end);
   virtual void OnImeConfirmComposition(
       const string16& text, const ui::Range& replacement_range);
   void OnPaintAtSize(const TransportDIB::Handle& dib_id,
                      int tag,
                      const gfx::Size& page_size,
                      const gfx::Size& desired_size);
-  void OnRepaint(const gfx::Size& size_to_paint);
+  void OnRepaint(gfx::Size size_to_paint);
   void OnSmoothScrollCompleted(int gesture_id);
   void OnSetTextDirection(WebKit::WebTextDirection direction);
   void OnGetFPS();
   void OnScreenInfoChanged(const WebKit::WebScreenInfo& screen_info);
   void OnUpdateScreenRects(const gfx::Rect& view_screen_rect,
                            const gfx::Rect& window_screen_rect);
 #if defined(OS_ANDROID)
   void OnImeBatchStateChanged(bool is_begin);
   void OnShowImeIfNeeded();
 #endif
@@ skipping 370 matching lines @@
   bool is_threaded_compositing_enabled_;
 
   base::WeakPtrFactory<RenderWidget> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderWidget);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_RENDER_WIDGET_H_