code: func globalLogTags(args *pb.RunnerArgs) map[string]string {
  	ret := make(map[string]string, 4)
  	ret[logDogViewerURLTag] = fmt.Sprintf("https://%s/build/%d", args.BuildbucketHost, args.Build.Id)
  
  	// SWARMING_SERVER is the full URL: https://example.com
  	// We want just the hostname.
  	env := environ.System()
  	if v, ok := env.Get("SWARMING_SERVER"); ok {
  		if u, err := url.Parse(v); err == nil && u.Host != "" {
  			ret["swarming.host"] = u.Host
  		}
  	}
  	if v, ok := env.Get("SWARMING_TASK_ID"); ok {
  		ret["swarming.run_id"] = v
  	}
  	if v, ok := env.Get("SWARMING_BOT_ID"); ok {
  		ret["swarming.bot_id"] = v
  	}
  	return ret
  }
docs: // globalLogTags returns tags to be added to all logdog streams by default.