tml";
    document.body.appendChild(iframe);
  });
}, "postMessaging to a same-origin iframe allows them to instantiate");

promise_test(t => {
  return new Promise(resolve => {
    const iframe = document.createElement("iframe");
    iframe.onload = t.step_func(() => {
      const level1 = iframe.contentWindow;
      const level2 = level1.frames[0];
      const level3 = level2.frames[0];
      const targetWindow = level3.frames[0];
      resolve(testSharingViaIncrementerScript(t, window, "window", targetWi