<!DOCTYPE html>
<title>Custom Elements: Create an element when definition is non-null and synchronous flag set</title>
<script src="../../resources/testharness.js"></script>
<script src="../../resources/testharnessreport.js"></script>
<script src="resources/custom-elements-helpers.js"></script>
<body>
<script>
'use strict';

function assert_rethrown(func, description) {
  assert_throws({ name: 'rethrown' }, () => {
    const err = new Error('check this is rethrown');
    err.name = 'rethrown';
    func(err)