LayoutTests/http/tests/security/mixedContent/resources/frame-with-insecure-image-secure-cookie-block.html

<script>
    document.cookie = "secureCookie=yes;secure";
</script>
<img src="http://127.0.0.1:8080/security/resources/compass.jpg">
<script>
console.log(document.cookie);
window.onload = function() {
    if (window.opener)
        window.opener.postMessage('done', '*');
};
</script>