mozilla-release/dom/media/tests/mochitest/test_getUserMedia_permission_iframe.html

<!DOCTYPE HTML>
<html>
<body>
<pre id="test">
<script type="application/javascript">
/**
  Runs inside iframe in test_getUserMedia_permission.html.
*/

const gUM = c => navigator.mediaDevices.getUserMedia(c);

(async () => {
  let message;
  let stream;
  try {
    stream = await gUM({ video: true });
    message = "success";
  } catch(e) {
    message = e.name;
  }
  parent.postMessage(message, "https://example.com:443");

  if (message == "success") {
    stream.getTracks().forEach(track => track.stop());
  }
})().catch(e => setTimeout(() => { throw e; }));
</script>
</pre>
</body>
</html>