Add a reason for configuring DTM for backup/rollback. In backup/rollback,

sync/internal_api/public/configure_reason.h

Index: sync/internal_api/public/configure_reason.h
diff --git a/sync/internal_api/public/configure_reason.h b/sync/internal_api/public/configure_reason.h
index 28a99f61cf97d3cbf3d4dc6e585493f61664a5a0..43784b773fd8008967d64e57e394c3d7503e3d47 100644
--- a/sync/internal_api/public/configure_reason.h
+++ b/sync/internal_api/public/configure_reason.h
@@ -32,6 +32,9 @@ enum ConfigureReason {
   // A configuration due to enabling or disabling encrypted types due to
   // cryptographer errors/resolutions.
   CONFIGURE_REASON_CRYPTO,
+
+  // Configure data types for backup/rollback.
+  CONFIGURE_REASON_BACKUP_ROLLBACK,
 };
 
 }  // namespace syncer