serving/xrefs: optimize common match-all filter
serving/xrefs: optimize common match-all filter

Reviewers: zarko, #core_team

Reviewed By: zarko, #core_team

Subscribers: #core_team

Differential Revision: https://phabricator-dot-kythe-repo.appspot.com/D1494

kythe/kythe,kythe/kythe,bzz/kythe,bzz/kythe,benjyw/kythe,kythe/kythe,kythe/kythe,benjyw/kythe,kythe/kythe,legrosbuffle/kythe,benjyw/kythe,benjyw/kythe,kythe/kythe,bzz/kythe,kythe/kythe,bzz/kythe,kythe/kythe,bzz/kythe,benjyw/kythe,legrosbuffle/kythe,bzz/kythe,benjyw/kythe,benjyw/kythe,bzz/kythe,bzz/kythe,legrosbuffle/kythe,benjyw/kythe,legrosbuffle/kythe,legrosbuffle/kythe,kythe/kythe,benjyw/kythe,legrosbuffle/kythe,bzz/kythe,legrosbuffle/kythe,kythe/kythe,legrosbuffle/kythe,bzz/kythe,benjyw/kythe,bzz/kythe,legrosbuffle/kythe,benjyw/kythe,bzz/kythe,legrosbuffle/kythe,kythe/kythe,benjyw/kythe,legrosbuffle/kythe