Implement notificationclose event

chrome/test/data/notifications/platform_notification_service.js

 // 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.
 
 // Service Worker to be used with the platform_notification_service.html page.
 var messagePort = null;
 
 addEventListener('message', function (event) {
   messagePort = event.data;
   messagePort.postMessage('ready');
 });
 
 // The notificationclick event will be invoked when a persistent notification
 // has been clicked on. When this happens, the title determines whether this
 // Service Worker has to act upon this.
 addEventListener('notificationclick', function (event) {
   if (event.notification.title == 'action_close')
     event.notification.close();
 
   messagePort.postMessage(event.notification.title);
 });
+
+// The notificationclose event will be invoked when a persistent notification
+// has been closed by the user.
+addEventListener('notificationclose', function (event) {
+  messagePort.postMessage('closing notification: ' + event.notification.title);
+});