Fix the issue that the top of fullscreen dialog is clipped away

The visibility of status bar comes from the top fullscreen window,
not from the focused window.
That has to be taken into account during the calculation of the
decor rect. You can use mTopIsFullscreen for this purpose.

Change-Id: I6159eb2ee389885cf5ab507157f9451841364d2f
[1/2] FB: Make menu unlock configurable