cc : Track opacity animation changes on effect tree

cc/trees/mutator_host_client.h

 // Copyright 2015 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 CC_TREES_MUTATOR_HOST_CLIENT_H_
 #define CC_TREES_MUTATOR_HOST_CLIENT_H_
 
 namespace gfx {
 class Transform;
 class ScrollOffset;
@@ skipping 27 matching lines @@
   virtual void SetElementScrollOffsetMutated(
       ElementId element_id,
       ElementListType list_type,
       const gfx::ScrollOffset& scroll_offset) = 0;
 
   virtual void ElementTransformIsPotentiallyAnimatingChanged(
       ElementId element_id,
       ElementListType list_type,
       bool is_animating) = 0;
 
+  virtual void ElementOpacityIsCurrentlyAnimatingChanged(
+      ElementId element_id,
+      bool is_currently_animating) {}
+
   virtual void ScrollOffsetAnimationFinished() = 0;
   virtual gfx::ScrollOffset GetScrollOffsetForAnimation(
       ElementId element_id) const = 0;
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_MUTATOR_HOST_CLIENT_H_