Fix issue #5050039: Launcher is sometimes rendering underneath the system/status bar

It looks like this is caused by the change in HC to stop activities when
the screen is off.  ViewRootImpl (a.k.a. ViewRoot) has special code to
avoid doing work when it is stopped, and it is now stopped when the screen
is off.  The problem here is if the window's activity is stopped when the
window is first displayed, then it would never do the initial fitSystemWindows()
with the status bar offsets given by the window manager, and never do this
again until the status bar changes.

Also included here is some re-arranging of the code dealing with the offsets
changing, because it was dealt with in two places and only one had a bunch of
code dealing with HW accelerated drawing and performing the fade transition
between states.  Now all of that is unified into one place.

Change-Id: I9828f02664cc622dbf186effb1f685a8aa4456a1