<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Security-Policy" content="block-all-mixed-content">
</head>
<body>
<script>
function frameLoaded() {
    if (window.opener)
        window.opener.postMessage("PASS did load data URL iframe.", "*");
}
</script>
<iframe onload="frameLoaded()" src="data:text/html,This is a boring HTML document."></iframe>
</body>
</html>