chromeos: Move files in //ash/common to //ash, part 2

ash/common/shelf/shelf_background_animator_observer.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_OBSERVER_H_
-#define ASH_COMMON_SHELF_SHELF_BACKGROUND_ANIMATOR_OBSERVER_H_
-
-#include "ash/ash_export.h"
-#include "third_party/skia/include/core/SkColor.h"
-
-namespace ash {
-
-// Observer for the ShelfBackgroundAnimator class.
-class ASH_EXPORT ShelfBackgroundAnimatorObserver {
- public:
-  // Called when the Shelf's background should be updated.
-  virtual void UpdateShelfBackground(SkColor color) {}
-
-  // Called when the Shelf item (aka button) backgrounds should be updated.
-  virtual void UpdateShelfItemBackground(SkColor color) {}
-
- protected:
-  virtual ~ShelfBackgroundAnimatorObserver() {}
-};
-
-}  // namespace ash
-
-#endif  // ASH_COMMON_SHELF_SHELF_BACKGROUND_ANIMATOR_OBSERVER_H_