LayoutTests/fast/harness/override-preferences.html

<html>
<body>
<script>
    if (window.testRunner) {
        testRunner.dumpAsText()
        testRunner.overridePreference("WebKitJavaScriptEnabled", false);
    }

    function loadstatus() {
        if (window.testRunner)
            document.getElementById("status").innerHTML = "FAIL";
    }
</script>
<body onload="loadstatus()">
    <p>This is a test that verifies that testRunner can have its default preferences overridden.  This test specifically checks that Javascript can be disabled, and you should see "PASS" below if viewing with a browser.</p>
    <span id="status">PASS</span>
</body>
</html>