Refactors animation to allow for cleaner subclassing. I'm doing this

app/linear_animation.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.
+// Inspired by NSAnimation
+
+#ifndef APP_LINEAR_ANIMATION_H_
+#define APP_LINEAR_ANIMATION_H_
+
+#include "app/animation.h"
+#include "base/time.h"
+
+class AnimationDelegate;
+
+// Linear time bounded animation. As the animation progresses AnimateToState is
+// invoked.
+class LinearAnimation : public Animation {
+ public:
+  // Initializes everything except the duration.
+  //
+  // Caller must make sure to call SetDuration() if they use this
+  // constructor; it is preferable to use the full one, but sometimes
+  // duration can change between calls to Start() and we need to
+  // expose this interface.
+  LinearAnimation(int frame_rate, AnimationDelegate* delegate);
+
+  // Initializes all fields.
+  LinearAnimation(int duration, int frame_rate, AnimationDelegate* delegate);
+
+  // Gets the value for the current state, according to the animation curve in
+  // use. This class provides only for a linear relationship, however subclasses
+  // can override this to provide others.
+  virtual double GetCurrentValue() const;
+
+  // Skip to the end of the current animation.
+  void End();
+
+  // Changes the length of the animation. This resets the current
+  // state of the animation to the beginning.
+  void SetDuration(int duration);
+
+ protected:
+  // Called when the animation progresses. Subclasses override this to
+  // efficiently update their state.
+  virtual void AnimateToState(double state) = 0;
+
+  // Invoked by the AnimationContainer when the animation is running to advance
+  // the animation. Use |time_now| rather than Time::Now to avoid multiple
+  // animations running at the same time diverging.
+  virtual void Step(base::TimeTicks time_now);
+
+  // Overriden to advance to the end (if End was invoked).
+  virtual void AnimationStopped();
+
+  // Overriden to return true if state is not 1.
+  virtual bool ShouldSendCanceledFromStop();
+
+ private:
+  base::TimeDelta duration_;
+
+  // Current state, on a scale from 0.0 to 1.0.
+  double state_;
+
+  // If true, we're in end. This is used to determine if the animation should
+  // be advanced to the end from AnimationStopped.
+  bool in_end_;
+
+  DISALLOW_COPY_AND_ASSIGN(LinearAnimation);
+};
+
+#endif  // APP_LINEAR_ANIMATION_H_