Spark TitleWindow should add a showCloseButton property

Steps to reproduce:
1. Try and compile the following <s:TitleWindow showCloseButton="false" />

Actual Results:
Compiler error. There is no showCloseButton property.

Expected Results:
Add showCloseButton property

Workaround (if any):
change the visible property on the closeButton skin part (shown below) or create a whole new custom skin.

<?xml version="1.0" encoding="utf-8"?>
<s:Application xmlns:fx="http://ns.adobe.com/mxml/2009"
xmlns:s="library://ns.adobe.com/flex/spark"
xmlns:mx="library://ns.adobe.com/flex/halo">

<fx:Script>
<![CDATA[
protected function chckBx_changeHandler(event:Event):void

{ ttlWndw.closeButton.visible = chckBx.selected; }

]]
>
</fx:Script>

<s:TitleWindow id="ttlWndw" title="The quick brown fox jumps over the lazy dog" width="

{sldr.value}

" height="200">
<s:controlBarContent>
<s:CheckBox id="chckBx" selected="true" change="chckBx_changeHandler(event);" />
<s:HSlider id="sldr" minimum="200" maximum="300" value="300" />
</s:controlBarContent>
</s:TitleWindow>

</s:Application>