Convert enable_pre_sync_backup flag to new flags system.

components/browser_sync/browser/profile_sync_service.cc

Index: components/browser_sync/browser/profile_sync_service.cc
diff --git a/components/browser_sync/browser/profile_sync_service.cc b/components/browser_sync/browser/profile_sync_service.cc
index 4ace5233f866735c2c165ea4f19d5ee831f13053..04cb9042b85be58c6aaf14fa571b64572450989d 100644
--- a/components/browser_sync/browser/profile_sync_service.cc
+++ b/components/browser_sync/browser/profile_sync_service.cc
@@ -49,6 +49,7 @@
 #include "components/sync_driver/signin_manager_wrapper.h"
 #include "components/sync_driver/sync_api_component_factory.h"
 #include "components/sync_driver/sync_client.h"
+#include "components/sync_driver/sync_driver_features.h"
 #include "components/sync_driver/sync_driver_switches.h"
 #include "components/sync_driver/sync_error_controller.h"
 #include "components/sync_driver/sync_stopped_reporter.h"
@@ -338,7 +339,7 @@ void ProfileSyncService::Initialize() {
     need_backup_ = false;
   }
 
-#if defined(ENABLE_PRE_SYNC_BACKUP)
+#if BUILDFLAG(ENABLE_PRE_SYNC_BACKUP)
   if (!running_rollback && !IsSignedIn()) {
     CleanUpBackup();
   }
@@ -2566,7 +2567,7 @@ void ProfileSyncService::ClearBrowsingDataSinceFirstSync() {
 void ProfileSyncService::CheckSyncBackupIfNeeded() {
   DCHECK_EQ(backend_mode_, SYNC);
 
-#if defined(ENABLE_PRE_SYNC_BACKUP)
+#if BUILDFLAG(ENABLE_PRE_SYNC_BACKUP)
   const base::Time last_synced_time = sync_prefs_.GetLastSyncedTime();
   // Check backup once a day.
   if (!last_backup_time_ &&