Because CMS does not support UseAdaptiveSizePolicy, code blocks guarded by UseAdaptiveSizePolicy are dead code in ParNewGeneration. This includes:
ParNewGeneration::_survivor_overflow and its accessor methods;
calls to size_policy->minor_collection_begin(), size_policy->minor_collection_end(), size_policy->avg_survived()->sample().

We should remove most code except minor_collection_begin() and minor_collection_end(), which could be used by UseGCOverheadLimit if it works for CMS in the future.