longtask-timing/longtask-detach-frame.html

<!DOCTYPE HTML>
<meta charset=utf-8>
<title>LongTask Timing: long task in nested child iframe</title>
<body>

<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="resources/utils.js"></script>

<h1>Long Tasks with detached iframe</h1>
<div id="log"></div>
<script>
  promise_test(async t => {
    assert_implements(window.PerformanceLongTaskTiming, 'Longtasks are not supported.');
    const iframe = document.createElement("iframe");
    document.body.appendChild(iframe);
    t.add_cleanup(() => iframe.remove());
    t.step_timeout(() => {
      busyWait();
      iframe.remove();
    });
}, 'Performance longtask entries dont crash when a frame is detached.');
</script>

</body>