Fix PiP dismissing on drag away from bottom and then fling

Adds two flags to watch for movement outside of the starting area of the
gesture, one for dismissing and one for minimizing.

Test: - Have PiP at bottom of screen, drag to top and fling down (does not
        dismiss)
      - Have PiP at left or right edge of screen, drag PiP to opposite
        edge and fling to other side (no longer minimizes)
Bug: 35358628

Change-Id: I007e2c2c688254dbe1abaecdedc28e281278def8