https://html.spec.whatwg.org/multipage/origin.html#attr-iframe-sandbox-allow-top-navigation-by-user-activation
// [2] https://html.spec.whatwg.org/multipage/media.html#allowed-to-play
promise_test(t => {
  const video = document.createElement('video');
  document.body.appendChild(video);
  t.add_cleanup(() => video.remove());
  return test_driver.bless('start video playback', () => {
    // `paused` changes before `play()` returns when "allowed to play", so the
    // promise, if any, is ignored.
    assert