17.5/ Remove synchronized calls, verify controller before finishing animation

- The states that trigger the call are all on the UI thread, so we
  shouldn't need to synchronize before calling into it.  But the
  second issue is that we set those states when the gesture ends and
  we calculate the end target.  This can happen before the animation
  started or after the animation has been canceled, so we need to
  guard against the null controller as well.

Bug: 143153963
Change-Id: I4649483a52c85c5662665d5e8905b49d5623b6dc