widget_observer_  346 ash/system/tray/tray_background_view.cc     GetWidget()->RemoveObserver(widget_observer_.get());
widget_observer_  350 ash/system/tray/tray_background_view.cc   GetWidget()->AddObserver(widget_observer_.get());
widget_observer_  178 ash/system/tray/tray_background_view.h   scoped_ptr<TrayWidgetObserver> widget_observer_;