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chromium/third_party/blink/web_tests/external/wpt/html/browsers/browsing-the-web/unloading-documents/support/beforeunload-sticky-start.html 

<!DOCTYPE html>
<meta charset="utf-8">
<title>Beforeunload must be gated behind sticky activation: start page</title>

<p>This page will immediately navigate. If a beforeunload dialog pops up, the test fails.</p>

<script>
window.onbeforeunload = e => e.preventDefault();
location.href = 'beforeunload-sticky-destination.html';
</script>