Function measure 

pub fn measure(
    types: &Types,
    id: RecordId,
    target: &TargetInfo,
    keying: Keying,
    granule: u64,
) -> Option<Tally>

Measures one record.

Returns nothing for a record that is not complete, since an incomplete one has no layout and no members to walk. A record too large to paint comes back as a tally that counts only its skip.