 global');

promise_test(async t => {
  assert_implements(supportsCustomizedBuiltinElements, 'customized built-in elements not supported');
  let w = await create_window_in_test(t, `<script>self.MyDivElement = class extends HTMLDivElement { constructor() { return document.createElement('div'); } };</`+`script>`);
  let w2 = await create_window_in_test(t);
  w2.customElements.define('my-div', w.MyDivElement, {extends: 'div'});
  let nextErrorPromise = nextErrorEvent([self, w, w2]);
  let elem = w2.document.c