[Sync] Moving DataTypeState to proto for serialization

sync/api/metadata_change_list.h

 // 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.
 
 #ifndef SYNC_API_METADATA_CHANGE_LIST_H_
 #define SYNC_API_METADATA_CHANGE_LIST_H_
 
 #include <string>
 
 #include "sync/base/sync_export.h"
 
 namespace sync_pb {
+class DataTypeState;
 class EntityMetadata;
 }  // namespace sync_pb
 
 namespace syncer_v2 {
-struct DataTypeState;
 
 // Interface used by the processor and service to communicate about metadata.
 // The purpose of the interface is to record changes to data type global and
 // per entity metadata for the purpose of propagating changes to the datatype
 // specific storage implementation.
 // The implementation of the interface is supposed to keep the record of all
 // updated / deleted metadata records and provide a mechanism to enumerate
 // them. If there are multiple UpdateMetadata / ClearMetadata calls made for the
 // same metadata record the last one is supposed to win.
 class SYNC_EXPORT MetadataChangeList {
  public:
   MetadataChangeList() {}
   virtual ~MetadataChangeList() {}
 
   // Requests DataTypeState to be updated in the storage.
-  virtual void UpdateDataTypeState(const DataTypeState& data_type_state) = 0;
+  virtual void UpdateDataTypeState(
+      const sync_pb::DataTypeState& data_type_state) = 0;
 
   // Requests DataTypeState to be cleared from the storage.
   virtual void ClearDataTypeState() = 0;
 
   // Requests metadata entry to be updated in the storage.
   // Please note that the update might contain a deleted entry if
   // metadata.is_deleted() is true (as opposed to clearing the entry from the
   // storage completely by calling the Clear method).
   virtual void UpdateMetadata(const std::string& client_tag,
                               const sync_pb::EntityMetadata& metadata) = 0;
 
   // Requests metadata entry to be cleared from the storage.
   virtual void ClearMetadata(const std::string& client_tag) = 0;
 };
 
 }  // namespace syncer_v2
 
 #endif  // SYNC_API_METADATA_CHANGE_LIST_H_