);
  iframe.contentDocument.body.appendChild(thirdDiv);
  const greenIframeSpan = thirdDiv.children[0];
  const redIframeSpan = thirdDiv.children[1];
  const blueIframeSpan = thirdDiv.children[2];
  const whiteIframeSpan = thirdDiv.children[3];
  const yellowIframeSpan = thirdDiv.children[4];

  const plainSheet = new CSSStyleSheet();
  const redStyleSheetPromise = plainSheet.replace(redStyleTexts[0]);
  return redStyleSheetPromise.then(function(redStyleSheet) {
    assert_throws_dom(
      'NotAllowedError