Extract the element implementation logic to function mods in <webview>.

extensions/renderer/resources/guest_view/app_view/app_view.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.
 
 var DocumentNatives = requireNative('document_natives');
 var GuestViewContainer = require('guestViewContainer').GuestViewContainer;
 var IdGenerator = requireNative('id_generator');
 
 function AppViewImpl(appviewElement) {
   GuestViewContainer.call(this, appviewElement, 'appview');
@@ skipping 52 matching lines @@
   this.guest.create(this.buildParams(), function() {
     if (!this.guest.getId()) {
       var errorMsg = 'Unable to connect to app "' + app + '".';
       window.console.warn(errorMsg);
       this.getErrorNode().innerText = errorMsg;
       if (callback) {
         callback(false);
       }
       return;
     }
-    this.attachWindow();
+    this.attachWindow$();
     if (callback) {
       callback(true);
     }
   }.bind(this));
 };
 
 GuestViewContainer.registerElement(AppViewImpl);