Aggregate damage rects in surface aggregator

cc/surfaces/surface.h

Index: cc/surfaces/surface.h
diff --git a/cc/surfaces/surface.h b/cc/surfaces/surface.h
index c76530b84699022095357268c2955b00809e2f1d..b12c34f911fee6367d78c0041f30e1144970a520 100644
--- a/cc/surfaces/surface.h
+++ b/cc/surfaces/surface.h
@@ -32,6 +32,9 @@ class CC_SURFACES_EXPORT Surface {
   // Returns the most recent frame that is eligible to be rendered.
   const CompositorFrame* GetEligibleFrame();
 
+  // Returns a number that increments by 1 every time a new frame is enqueued.
+  int frame_index() const { return frame_index_; }
+
   void RunDrawCallbacks();
 
   SurfaceFactory* factory() { return factory_; }
@@ -42,6 +45,7 @@ class CC_SURFACES_EXPORT Surface {
   SurfaceFactory* factory_;
   // TODO(jamesr): Support multiple frames in flight.
   scoped_ptr<CompositorFrame> current_frame_;
+  int frame_index_;
 
   base::Closure draw_callback_;