Use Flow Enum instead of brittle strings
Use Flow Enum instead of brittle strings

Summary: Does what it says on the tin.

Reviewed By: yuzhi

Differential Revision: D2873006

fb-gh-sync-id: 651935f0e08d41b963caa3f08ac09e0aa2680ba6

xuorig/relay,gabelevi/relay,facebook/relay,chirag04/relay,iamchenxin/relay,benjaminogles/relay,atxwebs/relay,mroch/relay,gabelevi/relay,atxwebs/relay,NevilleS/relay,voideanvalue/relay,voideanvalue/relay,voideanvalue/relay,zpao/relay,dbslone/relay,facebook/relay,kassens/relay,wincent/relay,apalm/relay,josephsavona/relay,josephsavona/relay,voideanvalue/relay,rosskevin/relay,kassens/relay,cesarandreu/relay,kassens/relay,xuorig/relay,freiksenet/relay,cesarandreu/relay,zpao/relay,facebook/relay,facebook/relay,wincent/relay,cpojer/relay,xuorig/relay,freiksenet/relay,iamchenxin/relay,chentsulin/relay,atxwebs/relay,mroch/relay,kassens/relay,chirag04/relay,benjaminogles/relay,venepe/relay,kassens/relay,freiksenet/relay,cesarandreu/relay,zpao/relay,xuorig/relay,cpojer/relay,rosskevin/relay,apalm/relay,facebook/relay,atxwebs/relay,voideanvalue/relay,wincent/relay,mroch/relay,venepe/relay,voideanvalue/relay,iamchenxin/relay,wincent/relay,venepe/relay,wincent/relay,chentsulin/relay,wincent/relay,NevilleS/relay,dbslone/relay,apalm/relay,facebook/relay,yungsters/relay,xuorig/relay,kassens/relay,benjaminogles/relay,NevilleS/relay,iamchenxin/relay,gabelevi/relay,yungsters/relay,cpojer/relay,chentsulin/relay,josephsavona/relay,xuorig/relay,cpojer/relay,yungsters/relay,chirag04/relay