Use MetadataChangeList and EntityChangeList in SharedModelTypeProcessor

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 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;
+
+  // 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_