It is time.

ui/views/animation/scroll_animator.h

-// Copyright (c) 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 UI_VIEWS_ANIMATION_SCROLL_ANIMATOR_H_
-#define UI_VIEWS_ANIMATION_SCROLL_ANIMATOR_H_
-
-#include "base/basictypes.h"
-#include "base/memory/scoped_ptr.h"
-#include "ui/gfx/animation/animation_delegate.h"
-#include "ui/views/views_export.h"
-
-namespace gfx {
-class SlideAnimation;
-}
-
-namespace views {
-
-class VIEWS_EXPORT ScrollDelegate {
- public:
-  // Returns true if the content was actually scrolled, false otherwise.
-  virtual bool OnScroll(float dx, float dy) = 0;
-
- protected:
-  ~ScrollDelegate() {}
-};
-
-class VIEWS_EXPORT ScrollAnimator : public gfx::AnimationDelegate {
- public:
-  // The ScrollAnimator does not own the delegate. Uses default acceleration.
-  explicit ScrollAnimator(ScrollDelegate* delegate);
-  virtual ~ScrollAnimator();
-
-  // Use this if you would prefer different acceleration than the default.
-  void set_acceleration(float acceleration) { acceleration_ = acceleration; }
-
-  void Start(float velocity_x, float velocity_y);
-  void Stop();
-
-  bool is_scrolling() const { return !!animation_.get(); }
-
- private:
-  // Implementation of gfx::AnimationDelegate.
-  virtual void AnimationEnded(const gfx::Animation* animation) override;
-  virtual void AnimationProgressed(const gfx::Animation* animation) override;
-  virtual void AnimationCanceled(const gfx::Animation* animation) override;
-
-  ScrollDelegate* delegate_;
-
-  float velocity_x_;
-  float velocity_y_;
-  float last_t_;
-  float duration_;
-  float acceleration_;
-
-  scoped_ptr<gfx::SlideAnimation> animation_;
-
-  DISALLOW_COPY_AND_ASSIGN(ScrollAnimator);
-};
-
-}  // namespace views
-
-#endif  // UI_VIEWS_ANIMATION_SCROLL_ANIMATOR_H_