[Sync] Remove ModelError::IsSet() in favor of base::Optional.

components/autofill/core/browser/webdata/autocomplete_sync_bridge.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_AUTOCOMPLETE_SYNC_BRIDGE_H_
 #define COMPONENTS_AUTOFILL_CORE_BROWSER_WEBDATA_AUTOCOMPLETE_SYNC_BRIDGE_H_
 
 #include <memory>
 #include <string>
 
+#include "base/optional.h"
 #include "base/scoped_observer.h"
 #include "base/supports_user_data.h"
 #include "base/threading/non_thread_safe.h"
 #include "components/autofill/core/browser/webdata/autofill_change.h"
 #include "components/autofill/core/browser/webdata/autofill_webdata_service_observer.h"
 #include "components/sync/model/metadata_change_list.h"
 #include "components/sync/model/model_error.h"
 #include "components/sync/model/model_type_sync_bridge.h"
 
 namespace autofill {
@@ skipping 15 matching lines @@
   static void CreateForWebDataServiceAndBackend(
       AutofillWebDataService* web_data_service,
       AutofillWebDataBackend* web_data_backend);
 
   static AutocompleteSyncBridge* FromWebDataService(
       AutofillWebDataService* web_data_service);
 
   // syncer::ModelTypeService implementation.
   std::unique_ptr<syncer::MetadataChangeList> CreateMetadataChangeList()
       override;
-  syncer::ModelError MergeSyncData(
+  base::Optional<syncer::ModelError> MergeSyncData(
       std::unique_ptr<syncer::MetadataChangeList> metadata_change_list,
       syncer::EntityDataMap entity_data_map) override;
-  syncer::ModelError ApplySyncChanges(
+  base::Optional<syncer::ModelError> ApplySyncChanges(
       std::unique_ptr<syncer::MetadataChangeList> metadata_change_list,
       syncer::EntityChangeList entity_changes) override;
   void GetData(StorageKeyList storage_keys, DataCallback callback) override;
   void GetAllData(DataCallback callback) override;
   // Generate a tag that uniquely identifies |entity_data| across all data
   // types. This is used to identify the entity on the server. The format, which
   // must remain the same for server compatibility, is:
   // "autofill_entry|$name|$value" where $name and $value are escaped.
   std::string GetClientTag(const syncer::EntityData& entity_data) override;
   // Generate a string key uniquely identifying |entity_data| in the context of
@@ skipping 23 matching lines @@
   // SupportsUserData, so it's guaranteed to outlive |this|.
   AutofillWebDataBackend* const web_data_backend_;
 
   ScopedObserver<AutofillWebDataBackend, AutocompleteSyncBridge>
       scoped_observer_;
 };
 
 }  // namespace autofill
 
 #endif  // COMPONENTS_AUTOFILL_CORE_BROWSER_WEBDATA_AUTOCOMPLETE_SYNC_BRIDGE_H_