[ash-md] Fixed ShelfBackgroundAnimator to not snap target values when being preempted.

ash/common/shelf/shelf_background_animator.h

 // Copyright 2016 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 ASH_COMMON_SHELF_SHELF_BACKGROUND_ANIMATOR_H_
 #define ASH_COMMON_SHELF_SHELF_BACKGROUND_ANIMATOR_H_
 
 #include <memory>
 #include <vector>
 
@@ skipping 64 matching lines @@
   //
   // NOTE: If a second request to paint the same |background_type| using the
   // BACKGROUND_CHANGE_ANIMATE change type is received it will be ignored and
   // observers will NOT be notified.
   void PaintBackground(ShelfBackgroundType background_type,
                        AnimationChangeType change_type);
 
   // gfx::AnimationDelegate:
   void AnimationProgressed(const gfx::Animation* animation) override;
   void AnimationEnded(const gfx::Animation* animation) override;
-  void AnimationCanceled(const gfx::Animation* animation) override;
 
  protected:
   // WmShelfObserver:
   void OnBackgroundTypeChanged(ShelfBackgroundType background_type,
                                AnimationChangeType change_type) override;
 
   // WallpaperControllerObserver:
   void OnWallpaperDataChanged() override;
   void OnWallpaperColorsChanged() override;
 
@@ skipping 82 matching lines @@
   AnimationValues item_background_values_;
 
   base::ObserverList<ShelfBackgroundAnimatorObserver> observers_;
 
   DISALLOW_COPY_AND_ASSIGN(ShelfBackgroundAnimator);
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_SHELF_SHELF_BACKGROUND_ANIMATOR_H_