[Sync] Fixing easy lint violations.

components/sync/core/simple_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 COMPONENTS_SYNC_CORE_SIMPLE_METADATA_CHANGE_LIST_H_
 #define COMPONENTS_SYNC_CORE_SIMPLE_METADATA_CHANGE_LIST_H_
 
 #include <map>
+#include <memory>
 #include <string>
 
 #include "components/sync/api/metadata_change_list.h"
 #include "components/sync/api/model_type_store.h"
 #include "components/sync/core/non_blocking_sync_common.h"
 #include "components/sync/protocol/data_type_state.pb.h"
 #include "components/sync/protocol/entity_metadata.pb.h"
 
 namespace syncer {
 
@@ skipping 37 matching lines @@
                        ModelTypeStore::WriteBatch* write_batch);
 
  private:
   MetadataChanges metadata_changes_;
   std::unique_ptr<DataTypeStateChange> state_change_;
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_CORE_SIMPLE_METADATA_CHANGE_LIST_H_