chromium/src/third_party/blink/web_tests/fast/dom/Window/resources/window-postmessage-user-gesture-frame.html

<script>
window.onmessage = function (event) {
    var msg = event.data;

    if (msg.consumeInFrame &&
        msg.count >= msg.consumeIndex &&
        window.open("about:blank", Math.random()))
        msg.consumeCount++;

    event.source.postMessage(msg, "*");
}
</script>