Add NotificationEvent.action property in SW events

Source/modules/notifications/NotificationEvent.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 NotificationEvent_h
 #define NotificationEvent_h
 
 #include "modules/EventModules.h"
 #include "modules/ModulesExport.h"
 #include "modules/notifications/Notification.h"
@@ skipping 15 matching lines @@
         return adoptRefWillBeNoop(new NotificationEvent(type, initializer));
     }
     static PassRefPtrWillBeRawPtr<NotificationEvent> create(const AtomicString& type, const NotificationEventInit& initializer, WaitUntilObserver* observer)
     {
         return adoptRefWillBeNoop(new NotificationEvent(type, initializer, observer));
     }
 
     ~NotificationEvent() override;
 
     Notification* notification() const { return m_notification.get(); }
+    String action() const { return m_action; }
 
     const AtomicString& interfaceName() const override;
 
     DECLARE_VIRTUAL_TRACE();
 
 private:
     NotificationEvent();
     NotificationEvent(const AtomicString& type, const NotificationEventInit&);
     NotificationEvent(const AtomicString& type, const NotificationEventInit&, WaitUntilObserver*);
 
     PersistentWillBeMember<Notification> m_notification;
+    String m_action;
 };
 
 } // namespace blink
 
 #endif // NotificationEvent_h