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

sync/internal_api/public/configure_reason.h

 // 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.
 
 #ifndef SYNC_INTERNAL_API_PUBLIC_CONFIGURE_REASON_H_
 #define SYNC_INTERNAL_API_PUBLIC_CONFIGURE_REASON_H_
 
 namespace syncer {
 
 // Note: This should confirm with the enums in sync.proto for
@@ skipping 14 matching lines @@
   // Setting up sync performs an initial config to download NIGORI data, and
   // also a config to download initial data once the user selects types.
   CONFIGURE_REASON_NEW_CLIENT,
 
   // A new datatype is enabled for syncing due to a client upgrade.
   CONFIGURE_REASON_NEWLY_ENABLED_DATA_TYPE,
 
   // 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
 
 #endif  // SYNC_INTERNAL_API_PUBLIC_CONFIGURE_REASON_H_