Summary: 1) Fixed MemTrackWorker::generations_in_used() calculation 2) Ensured NMT not to leak memory recorders after shutdown 3) Used ThreadCritical to block safepoint safe threads
Reviewed-by: acorn, coleenp, dholmes, kvn

7151532: DCmd for hotspot native memory tracking
Summary: Implementation of native memory tracking phase 1, which tracks VM native memory usage, and related DCmd
Reviewed-by: acorn, coleenp, fparain