Dispatch blur radius for BACKGROUND_APP state

When entering BACKGROUND_APP, it's possible that the blur radius will be
lost. We need to dispatch it on the first possible frame, otherwise
Overview won't have blurs.

Fixes: 196828055
Test: enter overview multiple times
Test: pull up all apps
Test: open app from home or all apps
Change-Id: I5920e1b28e2d23421863ecd59845e902040d126c