chromium/third_party/blink/web_tests/external/wpt/html/webappapis/dynamic-markup-insertion/opening-the-input-stream/resources/url-frame.html

<script>
onload = () => {
  const beforeURL = document.URL;
  document.open();
  const afterURL = document.URL;
  document.close();
  parent.testDone(beforeURL, afterURL);
}
</script>