Implement <appview> skeleton.

chrome/renderer/resources/extensions/web_view_deny.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.
 
 var DocumentNatives = requireNative('document_natives');
 
 // Output error message to console when using the <webview> tag with no
 // permission.
 var errorMessage = "You do not have permission to use the webview element." +
   " Be sure to declare the 'webview' permission in your manifest file.";
 
 // Registers <webview> custom element.
 function registerWebViewElement() {
   var proto = Object.create(HTMLElement.prototype);
 
   proto.createdCallback = function() {
-    console.error(errorMessage);
+    window.console.error(errorMessage);
   };
 
   window.WebView =
       DocumentNatives.RegisterElement('webview', {prototype: proto});
 
   // Delete the callbacks so developers cannot call them and produce unexpected
   // behavior.
   delete proto.createdCallback;
-  delete proto.enteredDocumentCallback;
-  delete proto.leftDocumentCallback;
+  delete proto.attachedCallback;
+  delete proto.detachedCallback;
   delete proto.attributeChangedCallback;
 }
 
 var useCapture = true;
 window.addEventListener('readystatechange', function listener(event) {
   if (document.readyState == 'loading')
     return;
 
   registerWebViewElement();
   window.removeEventListener(event.type, listener, useCapture);
 }, useCapture);