chrome/test/data/media/engagement/engagement_test_iframe_audio_child.html - chromium/src - Git at Google

 <!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>
	<!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>