engagement_test_iframe_audio_child.html

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

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