setUp() {
    wrapperDiv = dom.createDom(
        TagName.DIV, null, realIframe = dom.createDom(TagName.IFRAME));
    dom.appendChild(document.body, wrapperDiv);
    realIframeDoc = realIframe.contentWindow.document;
    propertyReplacer = new PropertyReplacer();
  }
@suppress {globalThis} suppression added to enable type
                       checking