Summary: Disallow increasing native memory tracking level
Reviewed-by: hseigel, ctornqvi, gtriantafill

Summary: Fixed memory leak in NMT by baselining memory in c heap instead of an arena.
Reviewed-by: coleenp, minqi

Summary: Enhance scalability of native memory tracking
Reviewed-by: coleenp, ctornqvi, gtriantafill