Reland - Replace FakeServer's implementation with LoopbackServer invocations.

components/sync/engine_impl/loopback_server/persistent_tombstone_entity.h

Index: components/sync/engine_impl/loopback_server/persistent_tombstone_entity.h
diff --git a/components/sync/engine_impl/loopback_server/persistent_tombstone_entity.h b/components/sync/engine_impl/loopback_server/persistent_tombstone_entity.h
index ea7236d13949176e6fe99888d918c5faad090226..0531666b0743b644d012502950bae7aef88aa8c6 100644
--- a/components/sync/engine_impl/loopback_server/persistent_tombstone_entity.h
+++ b/components/sync/engine_impl/loopback_server/persistent_tombstone_entity.h
@@ -20,9 +20,13 @@ class PersistentTombstoneEntity : public LoopbackServerEntity {
   ~PersistentTombstoneEntity() override;
 
   // Factory function for PersistentTombstoneEntity.
-  static std::unique_ptr<LoopbackServerEntity> Create(
+  static std::unique_ptr<LoopbackServerEntity> CreateFromEntity(
       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;
@@ -34,7 +38,11 @@ class PersistentTombstoneEntity : public LoopbackServerEntity {
  private:
   PersistentTombstoneEntity(const std::string& id,
                             int64_t version,
-                            const syncer::ModelType& model_type);
+                            const syncer::ModelType& model_type,
+                            const std::string& client_defined_unique_tag);
+
+  // The tag for this entity.
+  const std::string client_defined_unique_tag_;
 };
 
 }  // namespace syncer