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chromium/third_party/blink/web_tests/external/wpt/html/browsers/windows/auxiliary-browsing-contexts/resources/open-closer.html 

<!doctype html>
<meta charset="utf-8">
<html>
<body onload="openAuxiliary()">
<a rel="opener" target="_blank">Open auxiliary context that will close this window (its opener)</a>
<script src="/common/PrefixedLocalStorage.js"></script>
<script>
function openAuxiliary () {
  var prefixedLocalStorage = new PrefixedLocalStorageResource();
  var a = document.body.querySelector('a');
  a.href = prefixedLocalStorage.url('close-opener.html');
  document.body.append(a);
  a.click();
}
</script>
</body>
</html>