Ensured that the gut's bounds update properly

Because we were using a transition to update the content
and the guts were using getHeight() to infer their
actualHeight, getHeight() was returning the start
value of the animation and only updated later when other
state changed. This is now fixed by returning the
height determined in the layout.

Bug: 157215227
Test: add guts with 3 line priority, switch between them, observe correct measuring
Change-Id: Icdecd022276e1e21b78991cb5de9f3f7972cb490