[USS] Add SyncMetadataStore interface

components/autofill/core/browser/webdata/autofill_metadata_change_list.h

-// Copyright 2016 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_AUTOFILL_CORE_BROWSER_WEBDATA_AUTOFILL_METADATA_CHANGE_LIST_H_
-#define COMPONENTS_AUTOFILL_CORE_BROWSER_WEBDATA_AUTOFILL_METADATA_CHANGE_LIST_H_
-
-#include <string>
-
-#include "base/optional.h"
-#include "components/autofill/core/browser/webdata/autofill_table.h"
-#include "components/sync/base/model_type.h"
-#include "components/sync/model/metadata_change_list.h"
-#include "components/sync/model/model_error.h"
-#include "components/sync/model/sync_error.h"
-#include "components/sync/protocol/entity_metadata.pb.h"
-#include "components/sync/protocol/model_type_state.pb.h"
-
-namespace autofill {
-
-// A thin wrapper around an AutofillTable that implements sync's
-// MetadataChangeList interface. Changes are passed directly into the table and
-// not stored inside this object. Since the table calls can fail, |TakeError()|
-// must be called before this object is destroyed to check whether any
-// operations failed.
-class AutofillMetadataChangeList : public syncer::MetadataChangeList {
- public:
-  AutofillMetadataChangeList(AutofillTable* table, syncer::ModelType type);
-  ~AutofillMetadataChangeList() override;
-
-  // syncer::MetadataChangeList implementation.
-  void UpdateModelTypeState(
-      const sync_pb::ModelTypeState& model_type_state) override;
-  void ClearModelTypeState() override;
-  void UpdateMetadata(const std::string& storage_key,
-                      const sync_pb::EntityMetadata& metadata) override;
-  void ClearMetadata(const std::string& storage_key) override;
-
-  // Returns the value of |error_| and unsets it.
-  base::Optional<syncer::ModelError> TakeError();
-
- private:
-  // The autofill table to store metadata in; always outlives |this|.
-  AutofillTable* table_;
-
-  // The sync model type for this metadata.
-  syncer::ModelType type_;
-
-  // The first error encountered by this object, if any.
-  base::Optional<syncer::ModelError> error_;
-};
-
-}  // namespace autofill
-
-#endif  // COMPONENTS_AUTOFILL_CORE_BROWSER_WEBDATA_AUTOFILL_METADATA_CHANGE_LIST_H_