v1-distribution-disconnected-and-reconnected.html

<!DOCTYPE html>
<html>
<head>
  <script type="text/javascript" src="../resources/runner.js"></script>
  <script type="text/javascript" src="./v1-common.js"></script>
</head>
<body>
<div id="parent"></div>

<script>
const hostChildren = 500;
const host = createHostTreeWithDeepComponentChild(hostChildren);
document.querySelector('#parent').appendChild(host);
for (let i = 0; i < hostChildren; ++i) {
  host.children[i].id = i;
}

PerfTestRunner.measureTime({
  description: `Ensure slot assignment doesn't run for a disconnected and reconnected tree`,
  run: () => {
    for (let i = 0; i < hostChildren; ++i) {
      const firstChild = host.firstChild;
      firstChild.remove();
      firstChild.shadowRoot.querySelector('slot').assignedNodes();
      host.appendChild(firstChild);
      firstChild.shadowRoot.querySelector('slot').assignedNodes();
    }
    PerfTestRunner.assert_true(host.firstChild.id === "0", 'The test loop should end as it started');
  },
});
</script>
</body>
</html>

chromium/third_party/blink/perf_tests/shadow_dom/v1-distribution-disconnected-and-reconnected.html