Add reserve area to allocation stacks.

This fixes an issue with heap verification which was caused when
the allocation stack overflowed. This resulted in heap verification
failures since we were storing the newly allocated object in a
handle scope without having it be live either in the live bitmap
or allocation stack. We now push the object in the reserve area
before we do a GC due to allocation stack overflow.

Change-Id: I83b42c4b3250d7eaab1b49e53066e21c8656a740