<script>
window.addEventListener("message", function(e) {
    if (e.data == "set") {
        win = window.open("http://127.0.0.1:8000/security/frameNavigation/resources/ready.html", "targetWindow");
    } else if (e.data == "ready") {
        opener.postMessage("pass", "*");
    } else if (e.data == "cleanup") {
        win.close();
        opener.postMessage("done", "*");
    }
}, false);

opener.postMessage("ready", "*");
</script>
Helper window.