Add testRunner.cancelAllActiveNotifications to close all active notifications.

Source/testing/runner/NotificationPresenter.h

Index: Source/testing/runner/NotificationPresenter.h
diff --git a/Source/testing/runner/NotificationPresenter.h b/Source/testing/runner/NotificationPresenter.h
index 867eb813c385deb164c7c6dfbbf08dc36c86f914..837554b57c4bc05fec32870d77f69cb1ce5d08fd 100644
--- a/Source/testing/runner/NotificationPresenter.h
+++ b/Source/testing/runner/NotificationPresenter.h
@@ -55,6 +55,9 @@ public:
     // Called by the TestRunner to simulate a user clicking on a notification.
     bool simulateClick(const WebKit::WebString& notificationIdentifier);
 
+    // Called by the TestRunner to cancel all active notications.
+    void cancelAllActiveNotifications();
+
     // WebKit::WebNotificationPresenter interface
     virtual bool show(const WebKit::WebNotification&);
     virtual void cancel(const WebKit::WebNotification&);