CC Animation: Move ElementId from animation to trees.

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_
 
 // TODO(loyso) Move these headers out of cc/animation.
-#include "cc/animation/element_id.h"
 #include "cc/animation/property_animation_state.h"
 #include "cc/animation/target_property.h"
+#include "cc/trees/element_id.h"
 
 namespace gfx {
 class Transform;
 class ScrollOffset;
 }
 
 namespace cc {
 
 class FilterOperations;
 
@@ skipping 29 matching lines @@
       const PropertyAnimationState& state) = 0;
 
   virtual void ScrollOffsetAnimationFinished() = 0;
   virtual gfx::ScrollOffset GetScrollOffsetForAnimation(
       ElementId element_id) const = 0;
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_MUTATOR_HOST_CLIENT_H_