app: Remove animation header files.

app/animation_container_element.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_ELEMENT_H_
-#define APP_ANIMATION_CONTAINER_ELEMENT_H_
-#pragma once
-
-#include "base/time.h"
-
-// Interface for the elements the AnimationContainer contains. This is
-// implemented by Animation.
-class AnimationContainerElement {
- public:
-  // Sets the start of the animation. This is invoked from
-  // AnimationContainer::Start.
-  virtual void SetStartTime(base::TimeTicks start_time) = 0;
-
-  // Invoked when the animation is to progress.
-  virtual void Step(base::TimeTicks time_now) = 0;
-
-  // Returns the time interval of the animation. If an Element needs to change
-  // this it should first invoke Stop, then Start.
-  virtual base::TimeDelta GetTimerInterval() const = 0;
-
- protected:
-  virtual ~AnimationContainerElement() {}
-};
-
-#endif  // APP_ANIMATION_CONTAINER_ELEMENT_H_