chromium/third_party/blink/web_tests/fast/events/onunload-postmessage.html

<iframe id="x"></iframe>
<script>
if (window.testRunner)
    testRunner.dumpAsText();

window.onunload = function() {
    var frame = document.getElementById('x');
    frame.contentWindow.postMessage('foo', '*');
}
</script>
<p>TEST PASS: If this test doesn't leak when run with
--enable-leak-detection</p>