Improve apps v2 upgrade UX

remoting/webapp/crd/js/event_handlers.js

 // Copyright (c) 2012 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.
 
 'use strict';
 
 /** @suppress {duplicate} */
 var remoting = remoting || {};
 
 remoting.initGlobalEventHandlers = function() {
   window.addEventListener('resize', remoting.onResize, false);
   // When a window goes full-screen, a resize event is triggered, but the
   // Fullscreen.isActive call is not guaranteed to return true until the
   // full-screen event is triggered. In apps v2, the size of the window's
   // client area is calculated differently in full-screen mode, so register
   // for both events.
   remoting.fullscreen.addListener(remoting.onResize);
   if (!base.isAppsV2()) {
-    window.addEventListener('beforeunload', remoting.promptClose, false);
+    window.addEventListener('beforeunload', remoting.onBeforeUnload, false);
     window.addEventListener('unload', remoting.disconnect, false);
   }
 }
 
 /**
  * @param {Array.<{event: string, id: string,
  *     fn: function(Event):void}>} actions Array of actions to register.
  */
 function registerEventListeners(actions) {
   for (var i = 0; i < actions.length; ++i) {
@@ skipping 11 matching lines @@
 function registerEventListener(id, eventname, fn) {
   var element = document.getElementById(id);
   if (element) {
     element.addEventListener(eventname, fn, false);
   } else {
     console.error('Could not set ' + eventname +
         ' event handler on element ' + id +
         ': element not found.');
   }
 }