CrOS: Do not allow notifications to be added during shutdown.

chrome/browser/notifications/notification_test_util.h

Index: chrome/browser/notifications/notification_test_util.h
diff --git a/chrome/browser/notifications/notification_test_util.h b/chrome/browser/notifications/notification_test_util.h
index cbd6b82d4c9cc34e7ff68345e8e6b8c736370605..5b1b5b200c30b881cf94d1966c07b5acb7f1930e 100644
--- a/chrome/browser/notifications/notification_test_util.h
+++ b/chrome/browser/notifications/notification_test_util.h
@@ -70,6 +70,7 @@ class StubNotificationUIManager : public NotificationUIManager {
   bool CancelAllBySourceOrigin(const GURL& source_origin) override;
   bool CancelAllByProfile(ProfileID profile_id) override;
   void CancelAll() override;
+  void StartShutdown() override;
 
  private:
   using NotificationPair = std::pair<Notification, ProfileID>;
@@ -77,6 +78,8 @@ class StubNotificationUIManager : public NotificationUIManager {
 
   base::Closure notification_added_callback_;
 
+  bool is_shutdown_started_ = false;
+
   DISALLOW_COPY_AND_ASSIGN(StubNotificationUIManager);
 };