Use window.URL instead of window.webkitURL.

chrome/common/extensions/docs/examples/api/desktopCapture/app.js

 // Copyright 2013 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.
 
 function gotStream(stream) {
   console.log("Received local stream");
   var video = document.querySelector("video");
-  video.src = webkitURL.createObjectURL(stream);
+  video.src = URL.createObjectURL(stream);
   localstream = stream;
   stream.onended = function() { console.log("Ended"); };
 }
 
 function getUserMediaError() {
   console.log("getUserMedia() failed.");
 }
 
 function onAccessApproved(id) {
   if (!id) {
@@ skipping 12 matching lines @@
 document.querySelector('#start').addEventListener('click', function(e) {
   pending_request_id = chrome.desktopCapture.chooseDesktopMedia(
       ["screen", "window"], onAccessApproved);
 });
 
 document.querySelector('#cancel').addEventListener('click', function(e) {
   if (pending_request_id != null) {
     chrome.desktopCapture.cancelChooseDesktopMedia(pending_request_id);
   }
 });