Revert of Replaced BackgroundAnimator with ShelfBackgroundAnimator.

ash/common/shelf/overflow_button.h

Index: ash/common/shelf/overflow_button.h
diff --git a/ash/common/shelf/overflow_button.h b/ash/common/shelf/overflow_button.h
index b96479fbf4f856f10188d1758d54ca17d2699680..ac2a4faf2b65a1fa037eed75d7426d36c92500a6 100644
--- a/ash/common/shelf/overflow_button.h
+++ b/ash/common/shelf/overflow_button.h
@@ -20,9 +20,6 @@
   ~OverflowButton() override;
 
   void OnShelfAlignmentChanged();
-
-  // Sets alpha value of the background and schedules a paint.
-  void SetBackgroundAlpha(int alpha);
 
  private:
   // views::View:
@@ -61,9 +58,6 @@
   InkDropButtonListener* listener_;
   WmShelf* wm_shelf_;
 
-  // Alpha value used to paint the background.
-  int background_alpha_;
-
   DISALLOW_COPY_AND_ASSIGN(OverflowButton);
 };