Revert of [sync] Replace FakeServer's implementation with LoopbackServer invocations.

components/sync/engine_impl/loopback_server/persistent_tombstone_entity.h

 // Copyright 2014 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.
 
 #ifndef COMPONENTS_SYNC_ENGINE_IMPL_LOOPBACK_SERVER_PERSISTENT_TOMBSTONE_ENTITY_H_
 #define COMPONENTS_SYNC_ENGINE_IMPL_LOOPBACK_SERVER_PERSISTENT_TOMBSTONE_ENTITY_H_
 
 #include <memory>
 #include <string>
 
 #include "components/sync/base/model_type.h"
 #include "components/sync/engine_impl/loopback_server/loopback_server_entity.h"
 #include "components/sync/protocol/sync.pb.h"
 
 namespace syncer {
 
 // A Sync entity that represents a deleted item.
 class PersistentTombstoneEntity : public LoopbackServerEntity {
  public:
   ~PersistentTombstoneEntity() override;
 
   // Factory function for PersistentTombstoneEntity.
-  static std::unique_ptr<LoopbackServerEntity> CreateFromEntity(
+  static std::unique_ptr<LoopbackServerEntity> Create(
       const sync_pb::SyncEntity& id);
 
-  static std::unique_ptr<LoopbackServerEntity> CreateNew(
-      const std::string& id,
-      const std::string& client_defined_unique_tag);
-
   // LoopbackServerEntity implementation.
   bool RequiresParentId() const override;
   std::string GetParentId() const override;
   void SerializeAsProto(sync_pb::SyncEntity* proto) const override;
   bool IsDeleted() const override;
   sync_pb::LoopbackServerEntity_Type GetLoopbackServerEntityType()
       const override;
 
  private:
   PersistentTombstoneEntity(const std::string& id,
                             int64_t version,
-                            const syncer::ModelType& model_type,
-                            const std::string& client_defined_unique_tag);
-
-  // The tag for this entity.
-  const std::string client_defined_unique_tag_;
+                            const syncer::ModelType& model_type);
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_ENGINE_IMPL_LOOPBACK_SERVER_PERSISTENT_TOMBSTONE_ENTITY_H_