Add foreground profile changed to user switch observer.

Called when the focused activity changes from one profile
to another to allow sys ui to vary display based on the
current profile.
This reverts commit 735a3f90.
Resubmitting with fix for build break in another package.

Bug: 19531782
Change-Id: I98cd2968ade3b1d23feb90d98057f306695d569e