LayoutTests/fast/forms/empty-textarea-toggle-disabled.html

<p>Tests that toggling disabled state in a textarea leaves the textarea typeable.
To Test manually, load this page and type in the textarea. If you can type, then
the test succeeded.<p>
<textarea id="ta" disabled="disabled"></textarea>

<script type="text/javascript">
if (window.layoutTestController) {
    layoutTestController.dumpAsText();
    layoutTestController.waitUntilDone();
}

setTimeout(function() {
    ta.disabled = false;
    ta.focus();
    if (window.eventSender) {
        eventSender.keyDown('a', []);
        var result = ta.value;
        if (result == "a")
            document.write("<pre>SUCCESS</pre>");
        else
            document.write("<pre>FAIL, result was '" + result + "'.</pre>");
    }
    if (window.layoutTestController)
        layoutTestController.notifyDone();
}, 0);
</script>