size tracking can be done with a LengthSink and a tee. match tracking
was defeated by never having done any match tracking, all users would
see the same (empty) set of matches at all times. match tracking with
bytes offsets alone would not be sufficient in the general case, only
because computeHashModulo uses a single rewrite would it have worked.
Change-Id: Idb214b5222e0ea24f450f5505712a342b63d7570