Enable <adview> tag for packaged apps.

chrome/renderer/resources/extensions/platform_app.css

 /*
  * 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.
  *
  * A style sheet for Chrome apps.
  */
 
 @namespace "http://www.w3.org/1999/xhtml";
 
 body {
   -webkit-user-select: none;
   cursor: default;
 }
 
-webview {
+webview, adview {
   display: inline-block;
   width: 300px;
   height: 300px;
 }
 
 html, body {
   overflow: hidden;
 }
 
 img, a {
   -webkit-user-drag: none;
 }