Recycle mem-maps for collector transitions.

Recycle mem-maps for collector transitions.

We now create spaces when we need them for collector transitions or
homogeneous compaction by recycling mem maps. Change the bump
pointer space size to be as large as the heap capacity instead of
1/2 heap capacity like it used to be. For GSS, bump pointer spaces
are set to 32MB currently.

Changed GSS to have main space == non moving space since we don't
need to copy from the main space.

Fixes GC stress tests 074, 096.
Fixed test 080 oom throw with -Xmx2m for GC stress test, this was
broken since it was allocating a 4 MB array before starting the
OOM process.

Bug: 14059466
Bug: 16406852
Change-Id: I62877cfa24ec944a6f34ffac30334f454a8002fd