[logdog] Add Benchmark for Butler
[logdog] Add Benchmark for Butler

Result of cmd: `go test -cpu 1,4,8  -benchmem -benchtime 5s -bench .`
BenchmarkButler/10-streams    26991     223591 ns/op    71074 B/op    1077 allocs/op
BenchmarkButler/10-streams-4   7104     962387 ns/op   102146 B/op    1653 allocs/op
BenchmarkButler/10-streams-8   5599    1053311 ns/op   104747 B/op    1690 allocs/op
BenchmarkButler/100-streams    1575    3704459 ns/op  1147307 B/op   19032 allocs/op
BenchmarkButler/100-streams-4   486   12633191 ns/op  1714891 B/op   27574 allocs/op
BenchmarkButler/100-streams-8   448   13293517 ns/op  1762187 B/op   28092 allocs/op
BenchmarkButler/500-streams      96   59003737 ns/op  1932912 B/op  336447 allocs/op
BenchmarkButler/500-streams-4    34  166041286 ns/op  9512818 B/op  445303 allocs/op
BenchmarkButler/500-streams-8    32  172964215 ns/op  9907360 B/op  451898 allocs/op

R=iannucci

Change-Id: I724bcad706b1773e290b2b65fd046fce08ded0cc
Bug: 1077149
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/2174057
Commit-Queue: Yiwei Zhang <50b2a565e2e78c292794832469a30ce5abc9959c@google.com>
Auto-Submit: Yiwei Zhang <50b2a565e2e78c292794832469a30ce5abc9959c@google.com>
Reviewed-by: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go