Destroy SystemTrayDelegate in Shutdown()

BUG=140265
R=sadrul

Review URL: https://chromiumcodereview.appspot.com/10836094

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@150102 0039d316-1c4b-4281-b951-d872f2087c98

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_;