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 = URL.createObjectURL(stream);
  localstream = stream;
  stream.onended = function() { console.log("Ended"); };
}

function getUserMediaError() {
  console.log("getUserMedia() failed.");
}

function onAccessApproved(id) {
  if (!id) {
    console.log("Access rejected.");
    return;
  }
  navigator.webkitGetUserMedia({
      audio:false,
      video: { mandatory: { chromeMediaSource: "desktop",
                            chromeMediaSourceId: id } }
  }, gotStream, getUserMediaError);
}

var pending_request_id = null;

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);
  }
});

document.querySelector('#startFromBackgroundPage')
    .addEventListener('click', function(e) {
      chrome.runtime.sendMessage(
          {}, function(response) { console.log(response.farewell); });
    });