Track overview animation as atomic animation.

This fixed the bug where user can't double swipe up to All Apps. This is
needed before All Apps spring can be enabled, because the spring makes it
easier to get into this state.

To repo bug:
1. Hold shelf up so that overview starts to peek
2. Release
3. Before overview peek animation finishes, swipe up again to go to All Apps.

Bug: 79878197
Change-Id: I8c87b742d7da31d23be4decb72b45e9f21788af9