cc: Add support for partial swaps when using impl-side painting.

cc/layers/layer_impl.h

Index: cc/layers/layer_impl.h
diff --git a/cc/layers/layer_impl.h b/cc/layers/layer_impl.h
index 9af9eb5aa590ce200d403272baa45ee9293e8b7a..de24d91bd0b89723eb62067923c0cac96220d8b5 100644
--- a/cc/layers/layer_impl.h
+++ b/cc/layers/layer_impl.h
@@ -454,6 +454,10 @@ class CC_EXPORT LayerImpl : public LayerAnimationValueObserver,
 
   const gfx::RectF& update_rect() const { return update_rect_; }
 
+  void AddDamageRect(const gfx::RectF& damage_rect);
+
+  const gfx::RectF& damage_rect() const { return damage_rect_; }
+
   virtual base::DictionaryValue* LayerTreeAsJson() const;
 
   void SetStackingOrderChanged(bool stacking_order_changed);
@@ -652,6 +656,9 @@ class CC_EXPORT LayerImpl : public LayerAnimationValueObserver,
   // Uses layer (not content) space.
   gfx::RectF update_rect_;
 
+  // This rect is in layer space.
+  gfx::RectF damage_rect_;
+
   // Manages animations for this layer.
   scoped_refptr<LayerAnimationController> layer_animation_controller_;