Avoid sending empty OnRepaint msgs and propagate window damage correctly

content/renderer/gpu/render_widget_compositor.h

Index: content/renderer/gpu/render_widget_compositor.h
diff --git a/content/renderer/gpu/render_widget_compositor.h b/content/renderer/gpu/render_widget_compositor.h
index a4425267f4fdd74814bb0575ca7f0be23ff86742..76686da5f4cc46bff9096498d8c53d3e3deacd4f 100644
--- a/content/renderer/gpu/render_widget_compositor.h
+++ b/content/renderer/gpu/render_widget_compositor.h
@@ -11,6 +11,7 @@
 #include "cc/trees/layer_tree_settings.h"
 #include "skia/ext/refptr.h"
 #include "third_party/WebKit/Source/Platform/chromium/public/WebLayerTreeView.h"
+#include "ui/gfx/rect.h"
 
 class SkPicture;
 
@@ -39,6 +40,7 @@ class RenderWidgetCompositor : public WebKit::WebLayerTreeView,
                               bool enable_showing,
                               bool animate);
   void SetOverdrawBottomHeight(float overdraw_bottom_height);
+  void SetNeedsRedrawRect(gfx::Rect damage_rect);
 
   // WebLayerTreeView implementation.
   virtual void setSurfaceReady();