[Sync] Replace typedef with using.

components/sync/model/metadata_batch.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 COMPONENTS_SYNC_MODEL_METADATA_BATCH_H_
 #define COMPONENTS_SYNC_MODEL_METADATA_BATCH_H_
 
 #include <map>
 #include <string>
 
 #include "components/sync/protocol/entity_metadata.pb.h"
 #include "components/sync/protocol/model_type_state.pb.h"
 
 namespace syncer {
 
 // Map of storage keys to EntityMetadata proto.
-typedef std::map<std::string, sync_pb::EntityMetadata> EntityMetadataMap;
+using EntityMetadataMap = std::map<std::string, sync_pb::EntityMetadata>;
 
 // Container used to pass sync metadata from services to their processor.
 class MetadataBatch {
  public:
   MetadataBatch();
   virtual ~MetadataBatch();
 
   // Allows the caller to take ownership of the entire metadata map. This is
   // done because the caller will probably swap out all the EntityMetadata
   // protos from the map for performance reasons.
@@ skipping 10 matching lines @@
   void SetModelTypeState(const sync_pb::ModelTypeState& state);
 
  private:
   EntityMetadataMap metadata_map_;
   sync_pb::ModelTypeState state_;
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_MODEL_METADATA_BATCH_H_