Reland of "Apply Shelf/Dock opacity animations for the Material Design style."

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 7e3119ed71ba7ce9c57122915049e4fc51b405e1..b30f54d665240c46c5cb7174e210fbad54c0e850 100644
--- a/ash/shelf/shelf_view.cc
+++ b/ash/shelf/shelf_view.cc
@@ -805,6 +805,11 @@ void ShelfView::LayoutToIdealBounds() {
   overflow_button_->SetBoundsRect(ideal_bounds.overflow_bounds);
 }
 
+void ShelfView::UpdateShelfItemBackground(int alpha) {
+  GetAppListButton()->SetBackgroundAlpha(alpha);
+  overflow_button_->SetBackgroundAlpha(alpha);
+}
+
 void ShelfView::UpdateAllButtonsVisibilityInOverflowMode() {
   // The overflow button is not shown in overflow mode.
   overflow_button_->SetVisible(false);