Use window.URL instead of window.webkitURL.

chrome/common/extensions/docs/templates/articles/app_external.html

 <h1>External Content</h1>
 
 
 <p>
 The <a href="app_architecture.html#security">Chrome Apps security model</a> disallows
 external content in iframes and
 the use of inline scripting and <code>eval()</code>.
 You can override these restrictions,
 but your external content must be isolated from the app.
 </p>
@@ skipping 43 matching lines @@
 Fetch the remote URL into the app and serve its contents as a <code>blob:</code>
 URL:
 </p>
 
 <pre>
 var xhr = new XMLHttpRequest();
 xhr.open('GET', 'https://supersweetdomainbutnotcspfriendly.com/image.png', true);
 xhr.responseType = 'blob';
 xhr.onload = function(e) {
   var img = document.createElement('img');
-  img.src = window.webkitURL.createObjectURL(this.response);
+  img.src = window.URL.createObjectURL(this.response);
   document.body.appendChild(img);
 };
 
 xhr.send();
 </pre>
 
 <p>You may want to <a href="offline_apps.html#saving-locally">save</a>
 these resources locally, so that they are available offline.</p>
 
 <h2 id="webview">Embed external web pages</h2>
@@ skipping 215 matching lines @@
 
 <pre data-filename="sandboxed.html">
 var messageHandler = function(e) {
   console.log('Background script says hello.', e.data);
 };
 
 window.addEventListener('message', messageHandler);
 </pre>
 
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