[benchmark] BenchmarkDoctor: Optional markdown arg
[benchmark] BenchmarkDoctor: Optional markdown arg

Don't require the presence of `markdown` argument for initialization.
(It doesn't exist when BenchmarkDoctor is used from `run_smoke_bench`.)
sschiau/swift,glessard/swift,tkremenek/swift,benlangmuir/swift,amraboelela/swift,shahmishal/swift,airspeedswift/swift,allevato/swift,parkera/swift,shajrawi/swift,apple/swift,aschwaighofer/swift,gribozavr/swift,CodaFi/swift,benlangmuir/swift,austinzheng/swift,CodaFi/swift,xedin/swift,practicalswift/swift,CodaFi/swift,shajrawi/swift,xedin/swift,karwa/swift,rudkx/swift,danielmartin/swift,devincoughlin/swift,jckarter/swift,CodaFi/swift,gregomni/swift,allevato/swift,sschiau/swift,airspeedswift/swift,karwa/swift,gregomni/swift,JGiola/swift,gribozavr/swift,danielmartin/swift,aschwaighofer/swift,jmgc/swift,shajrawi/swift,xwu/swift,karwa/swift,danielmartin/swift,jmgc/swift,karwa/swift,harlanhaskins/swift,stephentyrone/swift,aschwaighofer/swift,practicalswift/swift,JGiola/swift,shajrawi/swift,rudkx/swift,karwa/swift,sschiau/swift,stephentyrone/swift,allevato/swift,ahoppen/swift,rudkx/swift,shahmishal/swift,amraboelela/swift,tkremenek/swift,devincoughlin/swift,parkera/swift,harlanhaskins/swift,shajrawi/swift,nathawes/swift,rudkx/swift,jckarter/swift,ahoppen/swift,nathawes/swift,practicalswift/swift,xedin/swift,tkremenek/swift,ahoppen/swift,airspeedswift/swift,devincoughlin/swift,atrick/swift,nathawes/swift,lorentey/swift,roambotics/swift,lorentey/swift,airspeedswift/swift,shahmishal/swift,xedin/swift,ahoppen/swift,austinzheng/swift,sschiau/swift,harlanhaskins/swift,jckarter/swift,sschiau/swift,harlanhaskins/swift,shajrawi/swift,lorentey/swift,parkera/swift,danielmartin/swift,rudkx/swift,apple/swift,glessard/swift,hooman/swift,nathawes/swift,practicalswift/swift,tkremenek/swift,practicalswift/swift,aschwaighofer/swift,glessard/swift,shahmishal/swift,airspeedswift/swift,parkera/swift,gregomni/swift,danielmartin/swift,hooman/swift,aschwaighofer/swift,practicalswift/swift,roambotics/swift,hooman/swift,sschiau/swift,apple/swift,roambotics/swift,tkremenek/swift,allevato/swift,jmgc/swift,apple/swift,practicalswift/swift,apple/swift,airspeedswift/swift,benlangmuir/swift,amraboelela/swift,atrick/swift,parkera/swift,xwu/swift,xwu/swift,amraboelela/swift,harlanhaskins/swift,benlangmuir/swift,roambotics/swift,stephentyrone/swift,devincoughlin/swift,jckarter/swift,JGiola/swift,glessard/swift,roambotics/swift,shahmishal/swift,parkera/swift,xwu/swift,tkremenek/swift,lorentey/swift,allevato/swift,devincoughlin/swift,lorentey/swift,austinzheng/swift,CodaFi/swift,shajrawi/swift,hooman/swift,devincoughlin/swift,gribozavr/swift,stephentyrone/swift,roambotics/swift,ahoppen/swift,jmgc/swift,harlanhaskins/swift,austinzheng/swift,gregomni/swift,xedin/swift,amraboelela/swift,gregomni/swift,atrick/swift,gribozavr/swift,sschiau/swift,karwa/swift,austinzheng/swift,gribozavr/swift,xedin/swift,shahmishal/swift,ahoppen/swift,hooman/swift,allevato/swift,devincoughlin/swift,shahmishal/swift,gribozavr/swift,benlangmuir/swift,austinzheng/swift,gregomni/swift,karwa/swift,lorentey/swift,jckarter/swift,airspeedswift/swift,atrick/swift,aschwaighofer/swift,nathawes/swift,JGiola/swift,CodaFi/swift,parkera/swift,xwu/swift,rudkx/swift,jmgc/swift,shahmishal/swift,karwa/swift,austinzheng/swift,gribozavr/swift,jmgc/swift,hooman/swift,aschwaighofer/swift,jckarter/swift,xedin/swift,benlangmuir/swift,hooman/swift,jmgc/swift,lorentey/swift,devincoughlin/swift,xedin/swift,JGiola/swift,amraboelela/swift,lorentey/swift,JGiola/swift,allevato/swift,danielmartin/swift,practicalswift/swift,danielmartin/swift,xwu/swift,stephentyrone/swift,stephentyrone/swift,atrick/swift,nathawes/swift,jckarter/swift,CodaFi/swift,glessard/swift,shajrawi/swift,glessard/swift,amraboelela/swift,gribozavr/swift,nathawes/swift,stephentyrone/swift,xwu/swift,sschiau/swift,atrick/swift,tkremenek/swift,parkera/swift,harlanhaskins/swift,apple/swift