Update background crop animation threshold

Empiric value for animation epsilon covers only the last
frame of the animation, which is not enough in some case.
This CL makes it a little bigger to cover two last frames.
The change is visually indistinguishable for user.

Bug: 63156733
Test: Go to/from recents with letterboxed app.
Change-Id: I42423527688dcb2dc157ae16bbe5b6de7eee3449