Migrate tsmon protos to proto3

common/tsmon/store/inmemory_test.go

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 package store
 
 import (
         "testing"
 
-        "github.com/golang/protobuf/proto"
         "github.com/luci/luci-go/common/tsmon/target"
         "golang.org/x/net/context"
 )
 
 func TestInMemory(t *testing.T) {
         ctx := context.Background()
         RunStoreImplementationTests(t, ctx, TestOptions{
                 Factory: func() Store {
-                        return NewInMemory(&target.Task{ServiceName: proto.String("default target")})
+                        return NewInMemory(&target.Task{ServiceName: "default target"})
                 },
                 RegistrationFinished: func(Store) {},
                 GetNumRegisteredMetrics: func(s Store) int {
                         return len(s.(*inMemoryStore).data)
                 },
         })
 }