esponse returns an opaque response from serviceworker and thus
    // the XHR must fail because it is not no-cors request.
    // Particularly, the XHR must not reuse the opaque response from the
    // preload request.
    xhr.onerror = function() {
      parent.done('PASS');
    };
    xhr.onload = function() {
      parent.done('FAIL: ' + xhr.responseText);
    };
    xhr.send();
  };
  l.onerror = function() {
    parent.done('FAIL: preload failed unexpectedly');
  };
  document.body.appendChild(l);
}
<