dock:: using xmousearea instead of guard window.

tower: https://tower.im/projects/8f19f0bf0e754f0b82ef2c24bc230973/todos/2f8f548b90a548f6b39cdb57344ff546/

Change-Id: Ib182b8b09d13b7c3dd6f00f0d64ac58995f39dfb