Diffusion - fix error log spew from D5894
Summary: forgot to declare this method as static. PHP manages to make it work functionally anyway. Ref T2784. Fixes T3175.
Test Plan: loaded diffusion, observed no errors
Reviewers: chad, epriestley
CC: aran, Korvin
Maniphest Tasks: T3175, T2784
Differential Revision: https://secure.phabricator.com/D5899