speculation-rules/prerender/resources/visibility-state-check.html

<!DOCTYPE html>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="utils.js"></script>
<script src="deferred-promise-utils.js"></script>
<script>
const params = new URLSearchParams(location.search);

// The main test page (visibility-state.html) loads the initiator page,
// then the initiator page will prerender itself with the `prerendering`
// parameter.
const isPrerendering = params.has('prerendering');

if (!isPrerendering) {
  loadInitiatorPage();
} else {
  const prerenderEventCollector = new PrerenderEventCollector();
  const promise = new Promise((resolve) => {
    prerenderEventCollector.addEvent(
        'Initial visibilityState: ' + document.visibilityState);

    document.addEventListener('prerenderingchange', () => {
      prerenderEventCollector.addEvent(
          'visibilityState after prerenderingchange: ' +
          document.visibilityState);
      resolve();
    });
  });
  prerenderEventCollector.start(promise, 'visibilityState check');
}

</script>