lled.', function() {
  let callbackWasCalled = false;
  customElements.polyfillWrapFlushCallback(f => {
    callbackWasCalled = true;
    assert(f instanceof Function);
    f();
  });
  customElements.define('x-test', class extends HTMLElement {});
  assert(callbackWasCalled);
});
</script>
</head>
<body></body>
</html>
