Revert of Use element id's for animations

cc/animation/animation_host.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_ANIMATION_ANIMATION_HOST_H_
 #define CC_ANIMATION_ANIMATION_HOST_H_
 
 #include <memory>
 #include <unordered_map>
 
@@ skipping 27 matching lines @@
 // Specifically, it owns all the AnimationTimelines objects.
 // There is just one AnimationHost for LayerTreeHost on main renderer thread
 // and just one AnimationHost for LayerTreeHostImpl on impl thread.
 // We synchronize them during the commit process in a one-way data flow process
 // (PushPropertiesTo).
 // An AnimationHost talks to its correspondent LayerTreeHost via
 // LayerTreeMutatorsClient interface.
 class CC_EXPORT AnimationHost {
  public:
   using ElementToAnimationsMap =
-      std::unordered_map<ElementId,
-                         scoped_refptr<ElementAnimations>,
-                         ElementIdHash>;
+      std::unordered_map<ElementId, scoped_refptr<ElementAnimations>>;
 
   static std::unique_ptr<AnimationHost> Create(ThreadInstance thread_instance);
   ~AnimationHost();
 
   void AddAnimationTimeline(scoped_refptr<AnimationTimeline> timeline);
   void RemoveAnimationTimeline(scoped_refptr<AnimationTimeline> timeline);
   AnimationTimeline* GetTimelineById(int timeline_id) const;
 
   void ClearTimelines();
 
@@ skipping 136 matching lines @@
 
   bool supports_scroll_animations_;
   bool animation_waiting_for_deletion_;
 
   DISALLOW_COPY_AND_ASSIGN(AnimationHost);
 };
 
 }  // namespace cc
 
 #endif  // CC_ANIMATION_ANIMATION_HOST_H_