Relay2: Add Environment#unstable_internal core API
Relay2: Add Environment#unstable_internal core API

Reviewed By: kassens

Differential Revision: D4348015

fbshipit-source-id: 7ce713c156aba2617ca79a368e1fd20bc669e9d9

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