healthcheck: client-side internal hook (#2378)
healthcheck: client-side internal hook (#2378)


grpc/grpc-go,thinkerou/grpc-go,dfawley/grpc-go,grpc/grpc-go,menghanl/grpc-go,stanley-cheung/grpc-go,stanley-cheung/grpc-go,thinkerou/grpc-go,dfawley/grpc-go,menghanl/grpc-go