CC Animation: Start replacing int layer_id with ElementId element_id.

cc/animation/animation_events.h

 // Copyright 2012 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_ANIMATION_ANIMATION_EVENTS_H_
 #define CC_ANIMATION_ANIMATION_EVENTS_H_
 
 #include <memory>
 #include <vector>
 
 #include "cc/animation/animation.h"
 #include "cc/animation/animation_curve.h"
 #include "cc/base/cc_export.h"
 #include "cc/output/filter_operations.h"
+#include "cc/trees/mutator_host_client.h"
 #include "ui/gfx/transform.h"
 
 namespace cc {
 
 struct CC_EXPORT AnimationEvent {
   enum Type { STARTED, FINISHED, ABORTED, PROPERTY_UPDATE, TAKEOVER };
 
   AnimationEvent(Type type,
-                 int layer_id,
+                 ElementId element_id,
                  int group_id,
                  TargetProperty::Type target_property,
                  base::TimeTicks monotonic_time);
 
   AnimationEvent(const AnimationEvent& other);
   AnimationEvent& operator=(const AnimationEvent& other);
 
   ~AnimationEvent();
 
   Type type;
-  int layer_id;
+  ElementId element_id;
   int group_id;
   TargetProperty::Type target_property;
   base::TimeTicks monotonic_time;
   bool is_impl_only;
   float opacity;
   gfx::Transform transform;
   FilterOperations filters;
 
   // For continuing a scroll offset animation on the main thread.
   double animation_start_time;
   std::unique_ptr<AnimationCurve> curve;
 };
 
 class CC_EXPORT AnimationEvents {
  public:
   AnimationEvents();
   ~AnimationEvents();
 
   std::vector<AnimationEvent> events_;
 };
 
 }  // namespace cc
 
 #endif  // CC_ANIMATION_ANIMATION_EVENTS_H_