Codebase Browser
chromium
Go to App

chromium/third_party/blink/web_tests/external/wpt/html/browsers/browsing-the-web/navigating-across-documents/resources/top-navigating-page.html 

<!DOCTYPE html>
<meta charset="utf-8">
<title>Page that navigates its top</title>
<script src=/common/get-host-info.sub.js></script>
<script>

let path = new URL("page-that-post-message-to-opener.html", window.location).pathname;
let fullUrl = get_host_info().HTTP_NOTSAMESITE_ORIGIN + path;
try {
  top.location = fullUrl;
} catch {
  top.opener.postMessage('Denied', '*');
}

</script>