<html>
<div>DIV</div>
<script>
    window.addEventListener("message", function(event) {
        var element = document.getElementsByTagName("div")[0];
        var xss = window.getMatchedCSSRules(element, "", false)[0].parentStyleSheet.foo;

        if (xss)
            alert("FAIL");
        else
            alert("PASS");
    
        if (window.testRunner)
            testRunner.notifyDone();
    }, false);
</script>
</html>