[Nirth]

package example
{
	import mx.containers.TitleWindow;

	public class Window extends TitleWindow
	{
		public function Window()
		{
			super();
		}
		
		override protected function initializationComplete():void
		{
			super.initializationComplete();
		}
		
		override protected function getHeaderHeight():Number
		{
			return 0;
		}
		
		override protected function layoutChrome(unscaledWidth:Number, unscaledHeight:Number):void
		{
			super.layoutChrome(unscaledWidth, unscaledHeight);
			
			titleBar.setActualSize(titleBar.width, 0);
		}
	}
}

По моему layoutChrome уже лишний, но времени проверять нема.