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

components/autofill/core/browser/webdata/autocomplete_sync_bridge.cc

 // 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.
 
 #include "components/autofill/core/browser/webdata/autocomplete_sync_bridge.h"
 
 #include <unordered_set>
 #include <utility>
 #include <vector>
 
@@ skipping 86 matching lines @@
   DCHECK(thread_checker_.CalledOnValidThread());
 }
 
 std::unique_ptr<syncer::MetadataChangeList>
 AutocompleteSyncBridge::CreateMetadataChangeList() {
   DCHECK(thread_checker_.CalledOnValidThread());
   return base::MakeUnique<AutofillMetadataChangeList>(GetAutofillTable(),
                                                       syncer::AUTOFILL);
 }
 
-syncer::ModelError AutocompleteSyncBridge::MergeSyncData(
+base::Optional<syncer::ModelError> AutocompleteSyncBridge::MergeSyncData(
     std::unique_ptr<syncer::MetadataChangeList> metadata_change_list,
     syncer::EntityDataMap entity_data_map) {
   DCHECK(thread_checker_.CalledOnValidThread());
   NOTIMPLEMENTED();
-  return syncer::ModelError();
+  return {};
 }
 
-syncer::ModelError AutocompleteSyncBridge::ApplySyncChanges(
+base::Optional<syncer::ModelError> AutocompleteSyncBridge::ApplySyncChanges(
     std::unique_ptr<syncer::MetadataChangeList> metadata_change_list,
     syncer::EntityChangeList entity_changes) {
   DCHECK(thread_checker_.CalledOnValidThread());
   NOTIMPLEMENTED();
-  return syncer::ModelError();
+  return {};
 }
 
 void AutocompleteSyncBridge::AutocompleteSyncBridge::GetData(
     StorageKeyList storage_keys,
     DataCallback callback) {
   DCHECK(thread_checker_.CalledOnValidThread());
   std::vector<AutofillEntry> entries;
   if (!GetAutofillTable()->GetAllAutofillEntries(&entries)) {
     change_processor()->ReportError(FROM_HERE,
                                     "Failed to load entries from table.");
@@ skipping 68 matching lines @@
     date_last_used = base::Time::FromInternalValue(*timestamps.rbegin());
   }
   return AutofillEntry(key, date_created, date_last_used);
 }
 
 AutofillTable* AutocompleteSyncBridge::GetAutofillTable() const {
   return AutofillTable::FromWebDatabase(web_data_backend_->GetDatabase());
 }
 
 }  // namespace autofill