Add a micro benchmark for context.WithValue() to compare using local and (#2986)
Add a micro benchmark for context.WithValue() to compare using local and (#2986)

global keys.
stanley-cheung/grpc-go,dfawley/grpc-go,stanley-cheung/grpc-go,menghanl/grpc-go,grpc/grpc-go,menghanl/grpc-go,grpc/grpc-go,dfawley/grpc-go