Introduce View.SYSTEM_UI_FLAG_IMMERSIVE_STICKY.

The existing View.SYSTEM_UI_FLAG_IMMERSIVE flag will be somewhat
redefined.  Swiping will clear the flags, revealing the normal bars.

The new View.SYSTEM_UI_FLAG_IMMERSIVE_STICKY flag will enable
hideybars - the auto-hiding, semi-transparent bar mode.

Bug:11062108
Change-Id: Ibf8be9072f0075953baa4580cd976e7562d44455