[USS] Add SyncMetadataStore interface

components/sync/model_impl/on_disk_metadata_change_list.h

-// Copyright 2016 The Chromium Authors. All rights reserved.
+// Copyright 2017 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_
+#ifndef COMPONENTS_SYNC_MODEL_IMPL_ON_DISK_METADATA_CHANGE_LIST_H_
+#define COMPONENTS_SYNC_MODEL_IMPL_ON_DISK_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/metadata_table.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 {
+namespace syncer {
 
-// A thin wrapper around an AutofillTable that implements sync's
+// A thin wrapper around an MetadataTable 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 {
+class OnDiskMetadataChangeList : public MetadataChangeList {

[pavely, 2017/04/06 22:56:42]

Both OnDiskMetadataChangeList and PassthroughMetadataChangeList persist metadata
on disk which makes their names not descriptive of their purpose. Both these
classes are really backed by other objects that perform IO operations
(MetadataTable and ModelTypeStore). I think names of these classes should
reflect that.
This one for example could be MetadataTableChangeList.

[Gang Wu, 2017/04/21 05:28:03]

Done.

  public:
-  AutofillMetadataChangeList(AutofillTable* table, syncer::ModelType type);
-  ~AutofillMetadataChangeList() override;
+  OnDiskMetadataChangeList(MetadataTable* table, syncer::ModelType type);
+  ~OnDiskMetadataChangeList() override;
 
-  // syncer::MetadataChangeList implementation.
+  // 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();
+  base::Optional<syncer::ModelError> TakeError() override;
 
  private:
-  // The autofill table to store metadata in; always outlives |this|.
-  AutofillTable* table_;
+  // The metadata table to store metadata in; always outlives |this|.
+  MetadataTable* 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
+}  // namespace syncer
 
-#endif  // COMPONENTS_AUTOFILL_CORE_BROWSER_WEBDATA_AUTOFILL_METADATA_CHANGE_LIST_H_
+#endif  // COMPONENTS_SYNC_MODEL_IMPL_ON_DISK_METADATA_CHANGE_LIST_H_