cument.body.appendChild(iframe);

  const iframe_reply = future(window, "message", iframe);
  iframe.contentDocument.write(check_sandbox_script);
  const result = await iframe_reply;
  iframe.remove();

  assert_equals(result.data, "document-domain-is-disallowed");
}, "initial empty document");

promise_test_parallel(async test => {
  const iframe = document.createElement("iframe");
  iframe.src = "data:text/html,dummy";

  const iframe_load_1 = future(iframe, "load");
  document.body.appendChild(iframe);
 