Replaced BackgroundAnimator with ShelfBackgroundAnimator.

ash/shelf/shelf_view.cc

Index: ash/shelf/shelf_view.cc
diff --git a/ash/shelf/shelf_view.cc b/ash/shelf/shelf_view.cc
index 7ca66f899f82331e54b2a0a6019718f54886a4f1..2d10e9ea653dec3181940b8c29fa985854b090a8 100644
--- a/ash/shelf/shelf_view.cc
+++ b/ash/shelf/shelf_view.cc
@@ -793,6 +793,11 @@ void ShelfView::PointerReleasedOnButton(views::View* view,
     drag_view_ = nullptr;
 }
 
+void ShelfView::UpdateShelfItemBackground(int alpha) {
+  GetAppListButton()->SetBackgroundAlpha(alpha);
+  overflow_button_->SetBackgroundAlpha(alpha);
+}
+
 void ShelfView::LayoutToIdealBounds() {
   if (bounds_animator_->IsAnimating()) {
     AnimateToIdealBounds();