Fix some issues with TwoButtonNavbarTouchController

- Use same swipe height as the tests use to get to Overview
- Use mStartState instead of fromState when determining
  target state, to disallow swiping through states, i.e.
  from NORMAL to OVERVIEW back to NORMAL in one long swipe
  up gesture. Instead, now swipe up from NORMAL goes to
  OVERVIEW and swipe up from OVERVIEW goes to NORMAL.

Fixes: 177316094
Change-Id: Ic8e9c8650d4cf11eec344802e3569413bfd5d7bc