[Sync] Implements the loopback sync server.

components/sync/engine_impl/loopback_server/persistent_unique_client_entity.h

Index: components/sync/engine_impl/loopback_server/persistent_unique_client_entity.h
diff --git a/components/sync/engine_impl/loopback_server/persistent_unique_client_entity.h b/components/sync/engine_impl/loopback_server/persistent_unique_client_entity.h
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index 0000000000000000000000000000000000000000..8e039002b68d3ab50c04d023bf207753105c5394
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+// 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_UNIQUE_CLIENT_ENTITY_H_
+#define COMPONENTS_SYNC_ENGINE_IMPL_LOOPBACK_SERVER_PERSISTENT_UNIQUE_CLIENT_ENTITY_H_
+
+#include <stdint.h>
+
+#include <memory>
+#include <string>
+
+#include "components/sync/base/model_type.h"
+#include "components/sync/engine_impl/loopback_server/loopback_server_entity.h"
+
+namespace sync_pb {
+class EntitySpecifics;
+class SyncEntity;
+}  // namespace sync_pb
+
+namespace syncer {
+
+// An entity that is unique per client account.
+//
+// TODO(pvalenzuela): Reconsider the naming of this class. In some cases, this
+// type is used to represent entities where the unique client tag is irrelevant
+// (e.g., Autofill Wallet).
+class PersistentUniqueClientEntity : public LoopbackServerEntity {
+ public:
+  PersistentUniqueClientEntity(const std::string& id,
+                               syncer::ModelType model_type,
+                               int64_t version,
+                               const std::string& name,
+                               const std::string& client_defined_unique_tag,
+                               const sync_pb::EntitySpecifics& specifics,
+                               int64_t creation_time,
+                               int64_t last_modified_time);
+
+  ~PersistentUniqueClientEntity() override;
+
+  // Factory function for creating a PersistentUniqueClientEntity.
+  static std::unique_ptr<LoopbackServerEntity> Create(
+      const sync_pb::SyncEntity& client_entity);
+
+  // Derives an ID from a unique client tagged entity.
+  static std::string EffectiveIdForClientTaggedEntity(
+      const sync_pb::SyncEntity& entity);
+
+  // LoopbackServerEntity implementation.
+  bool RequiresParentId() const override;
+  std::string GetParentId() const override;
+  void SerializeAsProto(sync_pb::SyncEntity* proto) const override;
+  sync_pb::LoopbackServerEntity_Type GetLoopbackServerEntityType()
+      const override;
+
+ private:
+  // These member values have equivalent fields in SyncEntity.
+  std::string client_defined_unique_tag_;
+  int64_t creation_time_;
+  int64_t last_modified_time_;
+};
+
+}  // namespace syncer
+
+#endif  // COMPONENTS_SYNC_ENGINE_IMPL_LOOPBACK_SERVER_PERSISTENT_UNIQUE_CLIENT_ENTITY_H_