We should make sure that the memory tracker classes have some constraints in place the give us confidence that they're working right. 
MemoryUsageTracker and SimpleMemoryUsageTracker  similar to this example here.

• delete the copy constructor, and the copy assignment constructor
• delete the move constructor too, if it isn't used at all
• Anything else that makes sense

There are probably already places where we violate those constraints, they can be addressed as part of this ticket.