cc: Cleanup class/struct forward declarations

cc/input/scrollbar_animation_controller_thinning.h

 // Copyright 2013 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_THINNING_H_
 #define CC_INPUT_SCROLLBAR_ANIMATION_CONTROLLER_THINNING_H_
 
 #include <memory>
 
 #include "base/macros.h"
 #include "cc/base/cc_export.h"
 #include "cc/input/scrollbar_animation_controller.h"
 
 namespace cc {
-class LayerImpl;
 
 // Scrollbar animation that partially fades and thins after an idle delay,
 // and reacts to mouse movements.
 class CC_EXPORT ScrollbarAnimationControllerThinning
     : public ScrollbarAnimationController {
  public:
   static std::unique_ptr<ScrollbarAnimationControllerThinning> Create(
       int scroll_layer_id,
       ScrollbarAnimationControllerClient* client,
       base::TimeDelta delay_before_starting,
@@ skipping 58 matching lines @@
   base::TimeDelta thinning_duration_;
 
   AnimatingProperty current_animating_property_;
 
   DISALLOW_COPY_AND_ASSIGN(ScrollbarAnimationControllerThinning);
 };
 
 }  // namespace cc
 
 #endif  // CC_INPUT_SCROLLBAR_ANIMATION_CONTROLLER_THINNING_H_