G1BarrierSet_merge
class G1CollectedHeap;
class G1HotCardCache;
class G1RemSetScanState;
class G1ParScanThreadState;
class G1Policy;
-class G1SATBCardTableModRefBS;
class G1ScanObjsDuringScanRSClosure;
class G1ScanObjsDuringUpdateRSClosure;
class HeapRegionClaimer;
// A G1RemSet in which each heap region has a rem set that records the