Make client tag IDs consistent in sync fake server

sync/test/fake_server/unique_client_entity.cc

Index: sync/test/fake_server/unique_client_entity.cc
diff --git a/sync/test/fake_server/unique_client_entity.cc b/sync/test/fake_server/unique_client_entity.cc
index 39d3a4c23d04069c4672d3ca937db02b6fe31332..11b37d585b657f46bd41e5ad3934e9bae19eae29 100644
--- a/sync/test/fake_server/unique_client_entity.cc
+++ b/sync/test/fake_server/unique_client_entity.cc
@@ -22,15 +22,13 @@ namespace fake_server {
 UniqueClientEntity::~UniqueClientEntity() { }
 
 // static
-FakeServerEntity* UniqueClientEntity::CreateNew(
+FakeServerEntity* UniqueClientEntity::Create(
     const sync_pb::SyncEntity& client_entity) {
   CHECK(client_entity.has_client_defined_unique_tag())
       << "A UniqueClientEntity must have a client-defined unique tag.";
   ModelType model_type =
       syncer::GetModelTypeFromSpecifics(client_entity.specifics());
-  string id = client_entity.version() == 0 ?
-      FakeServerEntity::CreateId(model_type, base::GenerateGUID()) :
-      client_entity.id_string();
+  string id = EffectiveIdForClientTaggedEntity(client_entity);
   return new UniqueClientEntity(id,
                                 model_type,
                                 client_entity.version(),
@@ -42,17 +40,11 @@ FakeServerEntity* UniqueClientEntity::CreateNew(
 }
 
 // static
-FakeServerEntity* UniqueClientEntity::CreateUpdatedVersion(
-    const sync_pb::SyncEntity& client_entity,
-    FakeServerEntity* current_server_entity) {
-  return new UniqueClientEntity(client_entity.id_string(),
-                                current_server_entity->GetModelType(),
-                                client_entity.version(),
-                                client_entity.name(),
-                                client_entity.client_defined_unique_tag(),
-                                client_entity.specifics(),
-                                client_entity.ctime(),
-                                client_entity.mtime());
+std::string UniqueClientEntity::EffectiveIdForClientTaggedEntity(
+    const sync_pb::SyncEntity& entity) {
+  return FakeServerEntity::CreateId(
+      syncer::GetModelTypeFromSpecifics(entity.specifics()),
+      entity.client_defined_unique_tag());
 }
 
 UniqueClientEntity::UniqueClientEntity(