Allow views to setSystemUiVisibility() with the same value and have it work.

This will save apps the trouble of having to first remove
the lights-out or hide-navigation flags before reapplying
them (in situations where the system UI has decided to
override those flags).

Bug: 5052456
Change-Id: I31f6ca9105379ae5f0216ebe3c39fc8d5d935f92