Destroy SystemTrayDelegate in Shutdown()

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 0729190acd9bcd61b89cf8a4e47a5d07aa7f41a9..2a9479247577dc91c0ff2c4c565f8f333f8b973a 100644
--- a/ash/system/status_area_widget.cc
+++ b/ash/system/status_area_widget.cc
@@ -305,6 +305,7 @@ void StatusAreaWidget::Shutdown() {
   // Destroy the trays early, causing them to be removed from the view
   // hierarchy. Do not used scoped pointers since we don't want to destroy them
   // in the destructor if Shutdown() is not called (e.g. in tests).
+  system_tray_delegate_.reset();
   delete system_tray_;
   system_tray_ = NULL;
   delete web_notification_tray_;