chromium/third_party/blink/web_tests/http/tests/security/secureContexts/resources/post-securecontext-status-on-msg.html

<script>
window.addEventListener("message", function () {
    if (window.top && window.top != window)
        window.top.postMessage({ "isSecureContext": window.isSecureContext }, "*");
});
window.parent.postMessage("add-csp", "*");
</script>