Fix growth limit / footprint limit problems

We now properly clear the growth limit of all the spaces when
ClearGrowthLimit is called. Previously we didn't clear the growth
limit of the background space.

This wasn't caught by heap test since it only manifested itself
when we had a zygote space.

Bug: 18504942
Change-Id: Ibb3d76cba54a45ef755d7e2ced8c2e16cd2996b0