app: Remove animation header files.

app/animation_container_observer.h

-// Copyright (c) 2010 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 APP_ANIMATION_CONTAINER_OBSERVER_H_
-#define APP_ANIMATION_CONTAINER_OBSERVER_H_
-#pragma once
-
-class AnimationContainer;
-
-// The observer is notified after every update of the animations managed by
-// the container.
-class AnimationContainerObserver {
- public:
-  // Invoked on every tick of the timer managed by the container and after
-  // all the animations have updated.
-  virtual void AnimationContainerProgressed(
-      AnimationContainer* container) = 0;
-
-  // Invoked when no more animations are being managed by this container.
-  virtual void AnimationContainerEmpty(AnimationContainer* container) = 0;
-
- protected:
-  virtual ~AnimationContainerObserver() {}
-};
-
-#endif  // APP_ANIMATION_CONTAINER_OBSERVER_H_