document-user-activation-iframe.html

<!DOCTYPE html>
<script>
internals.settings.setAutoplayPolicy('document-user-activation-required');

window.addEventListener('message', e => {
  if (e.data.command == 'play') {
    var video = document.createElement('video');
    video.play();
    window.parent.postMessage({
      result: !video.paused
    }, '*');
    video.pause();
  }
});
</script>

chromium/third_party/blink/web_tests/media/autoplay/resources/document-user-activation-iframe.html