Add NotificationEvent.action property in SW events

Source/modules/notifications/NotificationEvent.cpp

 // 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.
 
 #include "config.h"
 #include "modules/notifications/NotificationEvent.h"
+#include "wtf/text/WTFString.h"
 
 namespace blink {
 
 NotificationEvent::NotificationEvent()
+    : m_action(emptyString())
 {
 }
 
 NotificationEvent::NotificationEvent(const AtomicString& type, const NotificationEventInit& initializer)
     : ExtendableEvent(type, initializer)
+    , m_action(initializer.action())
 {
     if (initializer.hasNotification())
         m_notification = initializer.notification();
 }
 
 NotificationEvent::NotificationEvent(const AtomicString& type, const NotificationEventInit& initializer, WaitUntilObserver* observer)
     : ExtendableEvent(type, initializer, observer)
+    , m_action(initializer.action())
 {
     if (initializer.hasNotification())
         m_notification = initializer.notification();
 }
 
 NotificationEvent::~NotificationEvent()
 {
 }
 
 const AtomicString& NotificationEvent::interfaceName() const
 {
     return EventNames::NotificationEvent;
 }
 
 DEFINE_TRACE(NotificationEvent)
 {
     visitor->trace(m_notification);
     ExtendableEvent::trace(visitor);
 }
 
 } // namespace blink