PrepareForMarkCompact  714 src/mark-compact.cc     space->PrepareForMarkCompact();
PrepareForMarkCompact 2508 src/spaces.cc    PagedSpace::PrepareForMarkCompact();
PrepareForMarkCompact 1464 src/spaces.h     virtual void PrepareForMarkCompact();
PrepareForMarkCompact 2378 src/spaces.h     virtual void PrepareForMarkCompact();