LayoutTests/http/tests/web-locks/web-lock-in-srcdoc.html

<!DOCTYPE html>
<html>
<body>
<script>
if (window.testRunner) {
    testRunner.dumpAsText();
    testRunner.waitUntilDone();
    setTimeout(() => testRunner.notifyDone(), 3000);
}
onmessage = () => {
    result.textContent = 'PASS';
    if (window.testRunner)
        testRunner.notifyDone();
}
</script>
<p>This tests acquiring a web lock in srcdoc. You should see PASS below</p>
<div id="result">Running</div>
<iframe srcdoc="
<!DOCTYPE html>
<script>
navigator.locks.request('abc', {mode: 'shared'}, () => {
    top.postMessage('PASS', '*');
});
</script>"></iframe>
</body>
</html>