chromium/content/test/data/allowed_frames.html

<!DOCTYPE html>
<head>
</head>
<body>
  <!-- These frames should not have any other attributes, other than an id and
    those attributes required for testing feature policy creation and
    replication. See https://crbug.com/705658 -->
  <iframe id="child-0"></iframe>
  <iframe id="child-1" allow></iframe>
  <iframe id="child-2" allow="fullscreen; geolocation" src="/cross-site/bar.com/title1.html"></iframe>
  <iframe id="child-3" allow="fullscreen; geolocation" src="title1.html"></iframe>
</body>
</html>