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

ash/common/system/status_area_widget.cc

Index: ash/common/system/status_area_widget.cc
diff --git a/ash/common/system/status_area_widget.cc b/ash/common/system/status_area_widget.cc
index 0d95965a196a583603aeebaddb0e24fc68f0cc4e..ada0972c044099b15bee9984ef61c38a2b378c6f 100644
--- a/ash/common/system/status_area_widget.cc
+++ b/ash/common/system/status_area_widget.cc
@@ -154,6 +154,18 @@ void StatusAreaWidget::OnGestureEvent(ui::GestureEvent* event) {
   wm_shelf_->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);
+  ime_menu_tray_->UpdateShelfItemBackground(alpha);
+  palette_tray_->UpdateShelfItemBackground(alpha);
+#endif
+  overview_button_tray_->UpdateShelfItemBackground(alpha);
+}
+
 void StatusAreaWidget::AddSystemTray() {
   system_tray_ = new SystemTray(wm_shelf_);
   status_area_widget_delegate_->AddTray(system_tray_);