       let font_url = css_url + "&report-headers";

        let style = document.createElement("style");
        style.textContent = "@font-face { font-family: 'wpt'; font-style: normal; font-weight: normal; src: url(" + css_url + "); format('truetype'); } body { font-family: 'wpt';}";
        document.head.appendChild(style);
        return timeoutPromise(css_test, 1000)
          .then(() => requestViaXhr(font_url))
          .then(function(message) {
              assert_own_property(message, "headers");