Made some additional methods final.

Summary: Just some minor tidying up. I don't think that these methods should ever be overridden in subclasses.

Test Plan: N/A

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9569