Some random Web Notification cleanups

Source/modules/notifications/ServiceWorkerGlobalScopeNotifications.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef ServiceWorkerGlobalScopeNotifications_h
 #define ServiceWorkerGlobalScopeNotifications_h
 
 #include "core/events/EventTarget.h"
+#include "wtf/Allocator.h"
 
 namespace blink {
 
 class ServiceWorkerGlobalScopeNotifications {
+    STATIC_ONLY(ServiceWorkerGlobalScopeNotifications);
 public:
     DEFINE_STATIC_ATTRIBUTE_EVENT_LISTENER(notificationclick);
-    DEFINE_STATIC_ATTRIBUTE_EVENT_LISTENER(notificationerror);
 };
 
 } // namespace blink
 
 #endif // ServiceWorkerGlobalScopeNotifications_h