Modify hpack benchmark scenarios (#27567)
Modify hpack benchmark scenarios (#27567)

It used to be that we could run the hpack deserializer into an arbitrary
sink - that's about to change and the hpack deserializer will buffer
directly into a map. That being the case, it's really hard to compare
performance of the current and the new system. With this PR, I'm
updating the relevant scenario to be more similar to the eventual
scenario that we plan, so that as the new work finishes up, we can get a
clearer idea of what changes we're really making.
ejona86/grpc,grpc/grpc,nicolasnoble/grpc,nicolasnoble/grpc,stanley-cheung/grpc,stanley-cheung/grpc,nicolasnoble/grpc,ctiller/grpc,jtattermusch/grpc,grpc/grpc,vjpai/grpc,stanley-cheung/grpc,ejona86/grpc,nicolasnoble/grpc,jtattermusch/grpc,stanley-cheung/grpc,vjpai/grpc,jtattermusch/grpc,ctiller/grpc,ctiller/grpc,grpc/grpc,ejona86/grpc,ejona86/grpc,stanley-cheung/grpc,ctiller/grpc,ctiller/grpc,vjpai/grpc,nicolasnoble/grpc,vjpai/grpc,ejona86/grpc,grpc/grpc,ejona86/grpc,jtattermusch/grpc,stanley-cheung/grpc,nicolasnoble/grpc,jtattermusch/grpc,vjpai/grpc,ctiller/grpc,nicolasnoble/grpc,ctiller/grpc,stanley-cheung/grpc,vjpai/grpc,jtattermusch/grpc,grpc/grpc,ctiller/grpc,jtattermusch/grpc,stanley-cheung/grpc,stanley-cheung/grpc,ejona86/grpc,nicolasnoble/grpc,ejona86/grpc,nicolasnoble/grpc,grpc/grpc,stanley-cheung/grpc,jtattermusch/grpc,vjpai/grpc,jtattermusch/grpc,ctiller/grpc,grpc/grpc,jtattermusch/grpc,grpc/grpc,grpc/grpc,ctiller/grpc,vjpai/grpc,jtattermusch/grpc,ejona86/grpc,jtattermusch/grpc,vjpai/grpc,nicolasnoble/grpc,nicolasnoble/grpc,vjpai/grpc,ctiller/grpc,stanley-cheung/grpc,grpc/grpc,grpc/grpc,ejona86/grpc,nicolasnoble/grpc,grpc/grpc,ctiller/grpc,ejona86/grpc,ejona86/grpc,stanley-cheung/grpc,vjpai/grpc,vjpai/grpc