Merge Compositor's ScrollbarAnimationControllers into single class

cc/input/scrollbar_animation_controller_linear_fade.h

-// Copyright 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 CC_INPUT_SCROLLBAR_ANIMATION_CONTROLLER_LINEAR_FADE_H_
-#define CC_INPUT_SCROLLBAR_ANIMATION_CONTROLLER_LINEAR_FADE_H_
-
-#include <memory>
-
-#include "base/macros.h"
-#include "cc/base/cc_export.h"
-#include "cc/input/scrollbar_animation_controller.h"
-
-namespace cc {
-
-class CC_EXPORT ScrollbarAnimationControllerLinearFade
-    : public ScrollbarAnimationController {
- public:
-  static std::unique_ptr<ScrollbarAnimationControllerLinearFade> Create(
-      int scroll_layer_id,
-      ScrollbarAnimationControllerClient* client,
-      base::TimeDelta delay_before_starting,
-      base::TimeDelta resize_delay_before_starting,
-      base::TimeDelta duration);
-
-  ~ScrollbarAnimationControllerLinearFade() override;
-
-  void DidScrollUpdate(bool on_resize) override;
-
- protected:
-  ScrollbarAnimationControllerLinearFade(
-      int scroll_layer_id,
-      ScrollbarAnimationControllerClient* client,
-      base::TimeDelta delay_before_starting,
-      base::TimeDelta resize_delay_before_starting,
-      base::TimeDelta duration);
-
-  void RunAnimationFrame(float progress) override;
-  const base::TimeDelta& Duration() override;
-
- private:
-  float OpacityAtTime(base::TimeTicks now) const;
-  void ApplyOpacityToScrollbars(float opacity) override;
-
-  base::TimeDelta duration_;
-
-  DISALLOW_COPY_AND_ASSIGN(ScrollbarAnimationControllerLinearFade);
-};
-
-}  // namespace cc
-
-#endif  // CC_INPUT_SCROLLBAR_ANIMATION_CONTROLLER_LINEAR_FADE_H_