Fix non concurrent GC ergonomics.

If we dont have concurrent GC enabled, we need to force GC for alloc
when we hit the maximum allowed footprint so that our heap doesn't
keep growing until it hits the growth limit.

Refactored a bit of stuff.

Change-Id: I8eceac4ef01e969fd286ebde3a735a09d0a6dfc1
7 files changed