Update region sampling to account for window visibility

- Similar to the nav bar, we should also disable region sampling then
  the window is no longer visible (ie. when in immersive mode) otherwise
  we fall back into gpu composition which consumes more battery

Fixes: 268280575
Test: Enter immersive mode and verify region sampling is disabled
Change-Id: I99bf8986c6f22fd8d480d255d10cfcd39cfb79e3