permissions-policy-deferred-fetch.html

<!DOCTYPE html>
<script>
'use strict';

window.onload = () => {
  let enabled = true;
  try {
    fetchLater('/', {activateAfter: 0});
  } catch (e) {
    enabled = false;
  }
  parent.postMessage({ type: 'availability-result', enabled }, '*');
}
</script>

chromium/third_party/blink/web_tests/external/wpt/fetch/fetch-later/permissions-policy/resources/permissions-policy-deferred-fetch.html