Summary: It's an useful function. Plan to use it in another extension.
Test Plan: python ../../hg-crew/tests/run-tests.py --with-hg ../../hg-crew/hg test-manifestdiskcache.t
Reviewers: #sourcecontrol, lcharignon
Reviewed By: lcharignon
Subscribers: lcharignon, mitrandir
Differential Revision: https://phabricator.fb.com/D2896753
Signature: t1:2896753:1454542605:c660ee3e108b497c4a823bd732f98ebf5e147e02
