Pass through a const NativeCallStack& instead of a copy in:
MallocSiteHashtableEntry(const NativeCallStack& stack)
and let AllocationSite<MemoryCounter> accomplish the single copy into the _call_site member.
MallocSiteHashtableEntry(const NativeCallStack& stack)
and let AllocationSite<MemoryCounter> accomplish the single copy into the _call_site member.