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chromium/third_party/blink/web_tests/external/wpt/service-workers/service-worker/resources/clients-frame-freeze.html 

<!DOCTYPE html>
<script src="/resources/testdriver.js"></script>
<script src="/resources/testdriver-vendor.js"></script>
<script>
  document.addEventListener('freeze', () => {
      opener.postMessage('frozen', "*");
  });

  window.onmessage = (e) => {
    if (e.data == 'freeze') {
      test_driver.freeze();
    }
  };
  opener.postMessage('loaded', '*');
</script>