engagement_autoplay_iframe_test_frame.html

<!DOCTYPE html>
<meta charset="utf-8">
<title>Media Engagement Test</title>
<video autoplay src="engagement_valid_video.webm" id="video"></video>
<script>
document.getElementById("video").play().then(function() {
  parent.postMessage("Allowed", "*");
}, function() {
  parent.postMessage("Denied", "*");
});
</script>

chromium/chrome/test/data/media/engagement/engagement_autoplay_iframe_test_frame.html