code: func searchBuildset(buildset string, fields *field_mask.FieldMask) *buildbucketpb.SearchBuildsRequest {
  	return &buildbucketpb.SearchBuildsRequest{
  		Predicate: &buildbucketpb.BuildPredicate{
  			Tags: []*buildbucketpb.StringPair{{Key: "buildset", Value: buildset}},
  		},
  		Fields:   fields,
  		PageSize: 1000,
  	}
  }
docs: // searchBuildset creates a searchBuildsRequest that looks for a buildset tag.