chromium/third_party/blink/web_tests/http/tests/security/resources/agent-equality-same-origin.html

<!DOCTYPE html>
<html>
<head>
<title>Same origin test</title>
</head>
<body>
<iframe id="sub1" src="http://127.0.0.1:8000/security/resources/empty.html">
</iframe>
<iframe id="sub2" src="http://127.0.0.1:8000/security/resources/empty.html">
</iframe>
<script>
// This file should be loaded as an iframe hosted on 127.0.0.1:8000.

// This test creates two sibling subframes both located on 127.0.0.1:8000, and
// report the agent IDs of this document and two subframes.

function run(evt) {
  let sub1 = document.getElementById('sub1');
  let sub2 = document.getElementById('sub2');

  let message = [
    'same-origin test',
    internals.getAgentId(window),
    internals.getAgentId(sub1.contentWindow),
    internals.getAgentId(sub2.contentWindow)
  ];

  window.parent.postMessage(message, '*');
}

window.addEventListener('load', run, {'once': true});
</script>
</body>
</html>