ui: Clean up damaged rects and clear them after painting.

ui/compositor/layer.h

Index: ui/compositor/layer.h
diff --git a/ui/compositor/layer.h b/ui/compositor/layer.h
index 381e9829b3250a1207df29ff2a8cdaa969a4ff7c..bb8b1af6de89c7dd944136a3df2c4b080d88b62b 100644
--- a/ui/compositor/layer.h
+++ b/ui/compositor/layer.h
@@ -14,6 +14,7 @@
 #include "base/message_loop/message_loop.h"
 #include "cc/animation/animation_events.h"
 #include "cc/animation/layer_animation_event_observer.h"
+#include "cc/base/region.h"
 #include "cc/base/scoped_ptr_vector.h"
 #include "cc/layers/content_layer_client.h"
 #include "cc/layers/layer_client.h"
@@ -319,8 +320,9 @@ class COMPOSITOR_EXPORT Layer
   // Uses damaged rectangles recorded in |damaged_region_| to invalidate the
   // |cc_layer_|.
   void SendDamagedRects();
+  void ClearDamagedRects();
 
-  const SkRegion& damaged_region() const { return damaged_region_; }
+  const cc::Region& damaged_region() const { return damaged_region_; }
 
   void CompleteAllAnimations();
 
@@ -459,9 +461,9 @@ class COMPOSITOR_EXPORT Layer
   bool fills_bounds_opaquely_;
   bool fills_bounds_completely_;
 
-  // Union of damaged rects, in pixel coordinates, to be used when
-  // compositor is ready to paint the content.
-  SkRegion damaged_region_;
+  // Union of damaged rects, in layer space, to be used when compositor is ready
+  // to paint the content.
+  cc::Region damaged_region_;
 
   int background_blur_radius_;