Prepare Webview's browser plugin for coming Custom Elements API change.

chrome/renderer/resources/extensions/web_view.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.
 
 // Shim that simulates a <webview> tag via Mutation Observers.
 //
 // The actual tag is implemented via the browser plugin. The internals of this
 // are hidden via Shadow DOM.
 
 'use strict';
@@ skipping 817 matching lines @@
 
   proto.attributeChangedCallback = function(name, oldValue, newValue) {
     if (!this.internal_) {
       return;
     }
     var internal = this.internal_(secret);
     internal.handleBrowserPluginAttributeMutation_(name, newValue);
   };
 
   WebViewInternal.BrowserPlugin =
-      DocumentNatives.RegisterElement('browser-plugin', {prototype: proto});
+      DocumentNatives.RegisterElement('browser-plugin', {extends: 'object',
+                                                         prototype: proto});
 
   delete proto.createdCallback;
   delete proto.enteredDocumentCallback;
   delete proto.leftDocumentCallback;
   delete proto.attributeChangedCallback;
 }
 
 // Registers <webview> custom element.
 function registerWebViewElement() {
   var proto = Object.create(HTMLElement.prototype);
@@ skipping 83 matching lines @@
 
 /**
  * Implemented when the experimental API is available.
  * @private
  */
 WebViewInternal.prototype.maybeAttachWebRequestEventToWebview_ = function() {};
 
 exports.WebView = WebView;
 exports.WebViewInternal = WebViewInternal;
 exports.CreateEvent = CreateEvent;