Mask Problem with Flex Canvas and Drag Drop

100% Work
http://gravityblast.com/2009/07/12/mask-problem-with-flex-canvas-and-drag-drop/

Other Reference:
http://stackoverflow.com/questions/523571/how-to-make-the-canvas-clip-its-contents-in-flex
http://forums.adobe.com/message/199071#199071