Beginnings of synchronizing notifications in the notification database.

content/shell/browser/layout_test/layout_test_notification_manager.cc

Index: content/shell/browser/layout_test/layout_test_notification_manager.cc
diff --git a/content/shell/browser/layout_test/layout_test_notification_manager.cc b/content/shell/browser/layout_test/layout_test_notification_manager.cc
index a30c719b0f54904c8657db984816c327a083841c..057cc171300b28dedd5ff4d8e694a6f91c51f76b 100644
--- a/content/shell/browser/layout_test/layout_test_notification_manager.cc
+++ b/content/shell/browser/layout_test/layout_test_notification_manager.cc
@@ -97,6 +97,15 @@ void LayoutTestNotificationManager::ClosePersistentNotification(
   }
 }
 
+bool LayoutTestNotificationManager::GetDisplayedPersistentNotifications(
+    BrowserContext* browser_context,
+    std::set<std::string>* displayed_notifications) {
+  DCHECK(displayed_notifications);
+
+  // Notifications will never outlive the lifetime of running layout tests.
+  return false;
+}
+
 void LayoutTestNotificationManager::SimulateClick(const std::string& title) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);