CC Animation: Erase ElementAnimations::ObserverType.

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>
 
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
 #include "base/memory/ref_counted.h"
 #include "base/time/time.h"
 #include "cc/animation/animation.h"
 #include "cc/base/cc_export.h"
-#include "cc/trees/mutator_host_client.h"
 #include "ui/gfx/geometry/box_f.h"
 #include "ui/gfx/geometry/vector2d_f.h"
 
 namespace gfx {
 class ScrollOffset;
 }
 
 namespace cc {
 
 class AnimationEvents;
 class AnimationPlayer;
 class AnimationTimeline;
 class ElementAnimations;
 class LayerTreeHost;
+class MutatorHostClient;
+enum class LayerTreeType;
 
 enum class ThreadInstance { MAIN, IMPL };
 
 // An AnimationHost contains all the state required to play animations.
 // 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
@@ skipping 151 matching lines @@
 
   bool supports_scroll_animations_;
   bool animation_waiting_for_deletion_;
 
   DISALLOW_COPY_AND_ASSIGN(AnimationHost);
 };
 
 }  // namespace cc
 
 #endif  // CC_ANIMATION_ANIMATION_HOST_H_