Another StringRef -> std::string conversion fix.
Another StringRef -> std::string conversion fix.

This is needed to make this code compile on master-next.

stephentyrone/swift,CodaFi/swift,parkera/swift,hooman/swift,jckarter/swift,airspeedswift/swift,jmgc/swift,jckarter/swift,rudkx/swift,benlangmuir/swift,CodaFi/swift,xwu/swift,benlangmuir/swift,apple/swift,xwu/swift,xwu/swift,rudkx/swift,CodaFi/swift,airspeedswift/swift,hooman/swift,CodaFi/swift,roambotics/swift,stephentyrone/swift,parkera/swift,stephentyrone/swift,tkremenek/swift,gregomni/swift,roambotics/swift,ahoppen/swift,ahoppen/swift,roambotics/swift,allevato/swift,atrick/swift,parkera/swift,nathawes/swift,glessard/swift,jckarter/swift,hooman/swift,parkera/swift,apple/swift,allevato/swift,atrick/swift,airspeedswift/swift,tkremenek/swift,gregomni/swift,tkremenek/swift,apple/swift,xwu/swift,rudkx/swift,atrick/swift,atrick/swift,hooman/swift,nathawes/swift,JGiola/swift,allevato/swift,jmgc/swift,tkremenek/swift,apple/swift,parkera/swift,glessard/swift,hooman/swift,nathawes/swift,tkremenek/swift,allevato/swift,JGiola/swift,tkremenek/swift,glessard/swift,jckarter/swift,parkera/swift,gregomni/swift,tkremenek/swift,parkera/swift,stephentyrone/swift,hooman/swift,atrick/swift,gregomni/swift,ahoppen/swift,glessard/swift,stephentyrone/swift,airspeedswift/swift,roambotics/swift,jmgc/swift,benlangmuir/swift,CodaFi/swift,xwu/swift,jmgc/swift,roambotics/swift,nathawes/swift,JGiola/swift,jmgc/swift,rudkx/swift,airspeedswift/swift,airspeedswift/swift,benlangmuir/swift,stephentyrone/swift,rudkx/swift,CodaFi/swift,JGiola/swift,ahoppen/swift,allevato/swift,jckarter/swift,glessard/swift,nathawes/swift,benlangmuir/swift,apple/swift,hooman/swift,jckarter/swift,jmgc/swift,jckarter/swift,xwu/swift,roambotics/swift,jmgc/swift,ahoppen/swift,rudkx/swift,gregomni/swift,allevato/swift,JGiola/swift,nathawes/swift,apple/swift,stephentyrone/swift,CodaFi/swift,airspeedswift/swift,xwu/swift,parkera/swift,ahoppen/swift,atrick/swift,benlangmuir/swift,JGiola/swift,glessard/swift,nathawes/swift,gregomni/swift,allevato/swift