w Promise(resolve => iframe.onload = resolve);
  await test_driver.bless();

  iframe.contentDocument.querySelector('select').value = 'two';
  assert_equals(iframe.contentDocument.querySelector('select').value, 'two',
    'Assining two to select.value should work.');
  iframe.contentDocument.querySelector('form').submit();
  await new Promise(resolve => iframe.onload = resolve);

  await test_driver.bless();
  iframe.contentWindow.history.back();
  await new Promise(resolve => iframe.onload = resolve);
  aw