chromium/third_party/blink/web_tests/external/wpt/mixed-content/resources/blob-popup.html

<!DOCTYPE html>
<meta charset="utf-8">
<script>
  opener.postMessage({
      potentially_trustworthy: location.protocol === "https:",
      js_blob_url: URL.createObjectURL(
          new Blob([`const message = "Hello World!"`],
                   {type: 'application/javascript'})),
  }, "*");
</script>