minor refactor of FragmentResource.subscribeSpec
minor refactor of FragmentResource.subscribeSpec

Reviewed By: jstejada

Differential Revision: D17738682

fbshipit-source-id: 3215b72be28b8c3dab8bdd355f5bdbf7d583d6bc

facebook/relay,xuorig/relay,wincent/relay,voideanvalue/relay,xuorig/relay,voideanvalue/relay,wincent/relay,josephsavona/relay,facebook/relay,iamchenxin/relay,wincent/relay,voideanvalue/relay,voideanvalue/relay,xuorig/relay,wincent/relay,xuorig/relay,facebook/relay,cpojer/relay,voideanvalue/relay,atxwebs/relay,kassens/relay,iamchenxin/relay,kassens/relay,kassens/relay,yungsters/relay,facebook/relay,iamchenxin/relay,kassens/relay,kassens/relay,cpojer/relay,josephsavona/relay,xuorig/relay,josephsavona/relay,facebook/relay,atxwebs/relay,cpojer/relay,facebook/relay,yungsters/relay,voideanvalue/relay,kassens/relay,yungsters/relay,xuorig/relay,iamchenxin/relay,atxwebs/relay,wincent/relay,wincent/relay,atxwebs/relay,cpojer/relay