package  {
	
	import flash.display.Sprite;
	import net.hires.debug.Stats;
	import flash.events.MouseEvent;
	
	public class HiddenStats extends Sprite {
		
		private var _stats:Stats;

		public function HiddenStats() {
			
			_stats = new Stats();
			_stats.visible = true;
			_stats.alpha = 0;
			_stats.scaleX = _stats.scaleY = 0.1;
			_stats.x = 0;
			_stats.y = 0;
			_stats.doubleClickEnabled = true;
			_stats.useHandCursor = false;
			_stats.mouseEnabled = true;
			_stats.mouseChildren = false;
			_stats.buttonMode = true;
			_stats.addEventListener(MouseEvent.DOUBLE_CLICK, onStats_DOUBLE_CLICK);
			_stats.addEventListener(MouseEvent.MOUSE_DOWN, onStats_MOUSE_DOWN);
			_stats.addEventListener(MouseEvent.MOUSE_UP, onStats_MOUSE_UP);
			addChild(_stats);
		}
		
		private function onStats_DOUBLE_CLICK(event:MouseEvent):void
		{
			if (_stats.alpha < 1) {
				_stats.alpha = 1;
				_stats.scaleX = _stats.scaleY = 1;
				_stats.useHandCursor = true;
			} else {
				_stats.alpha = 0;
				_stats.scaleX = _stats.scaleY = 0.1;
				_stats.x = _stats.y = 0;
				_stats.useHandCursor = false;
			}
		}
		
		private function onStats_MOUSE_DOWN(event:MouseEvent):void
		{
			_stats.startDrag(false);
		}
		
		private function onStats_MOUSE_UP(event:MouseEvent):void
		{
			_stats.stopDrag();
		}
		
	}
	
}

package  {
	
	import flash.display.Sprite;
	import net.hires.debug.Stats;
	import flash.events.MouseEvent;
	
	public class HiddenStats extends Sprite {
		
		private var _stats:Stats;
		private var _secretHitAreaRect:int = 4;

		public function HiddenStats() {
			
			_stats = new Stats();
			_stats.visible = false;
			_stats.doubleClickEnabled = true;
			_stats.useHandCursor = true;
			_stats.mouseEnabled = true;
			_stats.mouseChildren = false;
			_stats.buttonMode = true;
			_stats.addEventListener(MouseEvent.DOUBLE_CLICK, onStats_DOUBLE_CLICK);
			_stats.addEventListener(MouseEvent.MOUSE_DOWN, onStats_MOUSE_DOWN);
			_stats.addEventListener(MouseEvent.MOUSE_UP, onStats_MOUSE_UP);
			addChild(_stats);
			
			stage.doubleClickEnabled = true;
			stage.addEventListener(MouseEvent.DOUBLE_CLICK, onStage_DOUBLE_CLICK);
		}
		
		
		private function onStats_DOUBLE_CLICK(event:MouseEvent):void
		{
			_stats.visible = false;
		}
		
		
		private function onStats_MOUSE_DOWN(event:MouseEvent):void
		{
			_stats.startDrag(false);
		}
		
		
		private function onStats_MOUSE_UP(event:MouseEvent):void
		{
			_stats.stopDrag();
		}
		
		
		private function onStage_DOUBLE_CLICK(event:MouseEvent):void
		{
			if ((mouseX < _secretHitAreaRect) && (mouseY < _secretHitAreaRect)) {
				_stats.visible = true;
				addChild(_stats);
			}
		}
		
		
		

	}
	
}

http://mrdoob.com/blog/post/582

For this to work you need get Mr.Doob's Stats class and put it in the 'net/hires/debug' package structure. This code basically makes the stats hidden until you double-click in the top-left corner of the stage. The stats are then draggable and can be hidden again by double-clicking the stats panel.

AS3 Have hidden performance stats which is made visible by double-clicking in the top-left corner of SWF

ActionScript 3