[Sync] Reimplement proto value conversions on top of field visitors.

components/sync/engine/cycle/sync_cycle_snapshot.cc

 // Copyright (c) 2012 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/sync/engine/cycle/sync_cycle_snapshot.h"
 
 #include <utility>
 
 #include "base/json/json_writer.h"
 #include "base/values.h"
@@ skipping 64 matching lines @@
   value->SetInteger("numServerOverwrites",
                     model_neutral_state_.num_server_overwrites);
   value->Set("downloadProgressMarkers",
              ProgressMarkerMapToValue(download_progress_markers_));
   value->SetBoolean("isSilenced", is_silenced_);
   // We don't care too much if we lose precision here, also.
   value->SetInteger("numEncryptionConflicts", num_encryption_conflicts_);
   value->SetInteger("numHierarchyConflicts", num_hierarchy_conflicts_);
   value->SetInteger("numServerConflicts", num_server_conflicts_);
   value->SetInteger("numEntries", num_entries_);
-  value->SetString("legacySource",
-                   GetUpdatesSourceString(legacy_updates_source_));
+  value->SetString("legacySource", ProtoEnumToString(legacy_updates_source_));
   value->SetBoolean("notificationsEnabled", notifications_enabled_);
 
   std::unique_ptr<base::DictionaryValue> counter_entries(
       new base::DictionaryValue());
   for (int i = FIRST_REAL_MODEL_TYPE; i < MODEL_TYPE_COUNT; i++) {
     std::unique_ptr<base::DictionaryValue> type_entries(
         new base::DictionaryValue());
     type_entries->SetInteger("numEntries", num_entries_by_type_[i]);
     type_entries->SetInteger("numToDeleteEntries",
                              num_to_delete_entries_by_type_[i]);
@@ skipping 60 matching lines @@
     const {
   return num_to_delete_entries_by_type_;
 }
 
 sync_pb::GetUpdatesCallerInfo::GetUpdatesSource
 SyncCycleSnapshot::legacy_updates_source() const {
   return legacy_updates_source_;
 }
 
 }  // namespace syncer