Move GuestView code from WebView-specific web_view_iframe.js into

extensions/renderer/resources/guest_view/guest_view_iframe_container.js

 // Copyright 2015 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.
 
 // --site-per-process overrides for guest_view_container.js
 
 var GuestViewContainer = require('guestViewContainer').GuestViewContainer;
+var IdGenerator = requireNative('id_generator');
 
 GuestViewContainer.prototype.createInternalElement$ = function() {
   var iframeElement = document.createElement('iframe');
   iframeElement.style.width = '100%';
   iframeElement.style.height = '100%';
   privates(iframeElement).internal = this;
   return iframeElement;
 };
+
+GuestViewContainer.prototype.attachWindow$ = function() {
+  var generatedId = IdGenerator.GetNextId();
+  // Generate an instance id for the container.
+  this.onInternalInstanceId(generatedId);
+  return true;
+};