chromium/third_party/blink/web_tests/external/wpt/client-hints/accept-ch-stickiness/resources/accept-ch.html

<html>
<body>

<!-- An empty webpage whose response headers include Accept-CH
header. Fetching this webpage should cause
user-agent to persist origin preferences for the client hints
specified in the Accept-CH header until a Clear-Site-Data header
is sent or user action is take to clear the session or data about
the origin.-->
<script>
  window.top.opener.postMessage('Loaded', '*');
</script>


</body>
</html>