Revert of Migrate tsmon protos to proto3

common/tsmon/field/field_test.go

Index: common/tsmon/field/field_test.go
diff --git a/common/tsmon/field/field_test.go b/common/tsmon/field/field_test.go
index 53b7f384fb028dc570b1273a089109fb76f98f2e..88a925245603fbf0b65ca6ceeadcf6f5b7ac5734 100644
--- a/common/tsmon/field/field_test.go
+++ b/common/tsmon/field/field_test.go
@@ -6,6 +6,8 @@
 import (
 	"fmt"
 	"testing"
+
+	"github.com/golang/protobuf/proto"
 
 	pb "github.com/luci/luci-go/common/tsmon/ts_mon_proto"
 
@@ -23,9 +25,9 @@
 			values: makeInterfaceSlice("v"),
 			want: []*pb.MetricsField{
 				{
-					Name:        "foo",
-					Type:        pb.MetricsField_STRING,
-					StringValue: "v",
+					Name:        proto.String("foo"),
+					Type:        pb.MetricsField_STRING.Enum(),
+					StringValue: proto.String("v"),
 				},
 			},
 		},
@@ -34,9 +36,9 @@
 			values: makeInterfaceSlice(int64(123)),
 			want: []*pb.MetricsField{
 				{
-					Name:     "foo",
-					Type:     pb.MetricsField_INT,
-					IntValue: 123,
+					Name:     proto.String("foo"),
+					Type:     pb.MetricsField_INT.Enum(),
+					IntValue: proto.Int64(123),
 				},
 			},
 		},
@@ -45,9 +47,9 @@
 			values: makeInterfaceSlice(true),
 			want: []*pb.MetricsField{
 				{
-					Name:      "foo",
-					Type:      pb.MetricsField_BOOL,
-					BoolValue: true,
+					Name:      proto.String("foo"),
+					Type:      pb.MetricsField_BOOL.Enum(),
+					BoolValue: proto.Bool(true),
 				},
 			},
 		},