[automerger skipped] Optimize RegionSpace::ClearFromSpace()
am: 17e5ba9850 -s ours
am skip reason: change_id Ie9e96c95a7ee78a9b18c1bfc26ed04acbe99c32b with SHA1 baa99adfc7 is in history

Change-Id: Ia52329f2698affa0fc15f98696e4cbae2b6c6c54