Replaced BackgroundAnimator with ShelfBackgroundAnimator.

ash/system/status_area_widget.cc

Index: ash/system/status_area_widget.cc
diff --git a/ash/system/status_area_widget.cc b/ash/system/status_area_widget.cc
index 57d82b6955f8f6262b7c7314627eed2e98ec5bb5..2e65f2bba1bb520d8528c6e285b4c7bdbcebbc81 100644
--- a/ash/system/status_area_widget.cc
+++ b/ash/system/status_area_widget.cc
@@ -147,6 +147,16 @@ void StatusAreaWidget::OnGestureEvent(ui::GestureEvent* event) {
     shelf_widget_->shelf_layout_manager()->UpdateAutoHideForGestureEvent(event);
 }
 
+void StatusAreaWidget::UpdateShelfItemBackground(int alpha) {
+  web_notification_tray_->UpdateShelfItemBackground(alpha);
+  system_tray_->UpdateShelfItemBackground(alpha);
+#if defined(OS_CHROMEOS)
+  virtual_keyboard_tray_->UpdateShelfItemBackground(alpha);
+  logout_button_tray_->UpdateShelfItemBackground(alpha);
+#endif
+  overview_button_tray_->UpdateShelfItemBackground(alpha);
+}
+
 void StatusAreaWidget::AddSystemTray() {
   system_tray_ = new SystemTray(this);
   status_area_widget_delegate_->AddTray(system_tray_);