iframe.contentDocument.body.textContent, "Initial body contents\n");
  }));
  iframe.onload = t.step_func_done(() => {
    assert_equals(iframe.contentDocument.body.textContent, "Initial body contents\n");
  });

  iframe.src = "module-tla-promise-iframe.html";
  document.body.appendChild(iframe);
});
</script>
