document.querySelector('#start').addEventListener('click', function(e) {
  pending_request_id = chrome.desktopCapture.chooseDesktopMedia(
      ["screen", "window"], onAccessApproved);
})

function onAccessApproved(id) {
  if (!id) {
    console.log("Access rejected.");
    return;
  }

  navigator.webkitGetUserMedia({
      audio:false,
      video: {
        mandatory: {
          chromeMediaSource: "desktop",
          chromeMediaSourceId: id,
          minWidth: "536",
          minHeight: "150",
          maxWidth: "536",
          maxHeight: "150"
        }
      }
  }, gotStream, getUserMediaError);
}