Report layer boost at all levels, not just Activity

Now that app transitions are hierarchical, the boost info
should be read at all levels because it is only set on levels
which are animating.

Bug: 159473343
Test: Use non-resizable home-screen with split apps and dismiss
      secondary app -- observe that it animates above home.
Change-Id: Ie1f883486e0dd36256764197690525cf3762dc4d