chromium/third_party/blink/web_tests/http/tests/security/frameNavigation/resources/popup-ready-to-navigate-child.html

<script>
var f = window.frames;
function go() {
    f[0].location = "http://127.0.0.1:8000/security/frameNavigation/resources/fail.html";
}
opener.postMessage("ready", "*");
</script>