third_party/blink/web_tests/http/tests/security/srcdoc-can-access-parent.html

<script>
if (window.testRunner) {
    testRunner.dumpAsText();
}
</script>
<div id="result">Waiting...</div>
<iframe srcdoc="
    Trying to access parent...
    <script>
    parent.document.getElementById('result').innerHTML = 'PASS';
    </script>
"></iframe>