Revert of Replaced BackgroundAnimator with ShelfBackgroundAnimator.

ash/common/shelf/shelf_background_animator_observer.h

Index: ash/common/shelf/shelf_background_animator_observer.h
diff --git a/ash/common/shelf/shelf_background_animator_observer.h b/ash/common/shelf/shelf_background_animator_observer.h
deleted file mode 100644
index b90e8814ed1443773aaf6033438962c25fd299f6..0000000000000000000000000000000000000000
--- a/ash/common/shelf/shelf_background_animator_observer.h
+++ /dev/null
@@ -1,31 +0,0 @@
-// 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"
-
-namespace ash {
-
-// Observer for the ShelfBackgroundAnimator class.
-class ASH_EXPORT ShelfBackgroundAnimatorObserver {
- public:
-  // Called when the Shelf's opaque background should be updated.
-  virtual void UpdateShelfOpaqueBackground(int alpha) {}
-
-  // Called when the Shelf's asset based background should be updated.
-  // TODO(bruthig): Remove when non-md is no longer needed (crbug.com/614453).
-  virtual void UpdateShelfAssetBackground(int alpha) {}
-
-  // Called when the Shelf item (aka button) backgrounds should be updated.
-  virtual void UpdateShelfItemBackground(int alpha) {}
-
- protected:
-  virtual ~ShelfBackgroundAnimatorObserver() {}
-};
-
-}  // namespace ash
-
-#endif  // ASH_COMMON_SHELF_SHELF_BACKGROUND_ANIMATOR_OBSERVER_H_