Generate an internal SBE command for statistics analysis which runs the equivalent of 

db.coll.aggregate( [
   { $project: {val : path} },
   { $_analyzeInternal: {} },
   { $merge: ... }
]);

 
_analyzeInternal will be implemented in a follow-on ticket. For now it can simply consume values and emit an empty document at the end of the stream.

The $merge is to replace (or insert) the value in the stats collection with the newly calculated value. Note that this requires a unique index on "path" which should be workable.