fixup! Add support for runtime toggle of navbar

* Due to race condition we end up calling
  DisplayPolicy.hasNavigationBar() before
  the settings value is updated.
* Switch over few more navigation bar
  checks that'd likely also fail.
* Call WindowManagerService.onOverlayChanged()
  so that we don't end up with reserved
  space for 3-button style navbar when gestural
  navigation is enabled.

Change-Id: I46ffe56b8fe8b3fe94629915a636b6cdeaa0b50d