Add an action for server to send down rollback command.

sync/internal_api/public/util/syncer_error.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 "sync/internal_api/public/util/syncer_error.h"
 
 #include "base/logging.h"
 
 namespace syncer {
 
 #define ENUM_CASE(x) case x: return #x; break;
 const char* GetSyncerErrorString(SyncerError value) {
   switch (value) {
     ENUM_CASE(UNSET);
     ENUM_CASE(CANNOT_DO_WORK);
     ENUM_CASE(NETWORK_CONNECTION_UNAVAILABLE);
     ENUM_CASE(NETWORK_IO_ERROR);
     ENUM_CASE(SYNC_SERVER_ERROR);
     ENUM_CASE(SYNC_AUTH_ERROR);
     ENUM_CASE(SERVER_RETURN_INVALID_CREDENTIAL);
     ENUM_CASE(SERVER_RETURN_UNKNOWN_ERROR);
     ENUM_CASE(SERVER_RETURN_THROTTLED);
     ENUM_CASE(SERVER_RETURN_TRANSIENT_ERROR);
     ENUM_CASE(SERVER_RETURN_MIGRATION_DONE);
     ENUM_CASE(SERVER_RETURN_CLEAR_PENDING);
     ENUM_CASE(SERVER_RETURN_NOT_MY_BIRTHDAY);
     ENUM_CASE(SERVER_RETURN_CONFLICT);
     ENUM_CASE(SERVER_RESPONSE_VALIDATION_FAILED);
     ENUM_CASE(SERVER_RETURN_DISABLED_BY_ADMIN);
+    ENUM_CASE(SERVER_RETURN_USER_ROLLBACK);
     ENUM_CASE(SERVER_MORE_TO_DOWNLOAD);
     ENUM_CASE(DATATYPE_TRIGGERED_RETRY);
     ENUM_CASE(SYNCER_OK);
   }
   NOTREACHED();
   return "INVALID";
 }
 #undef ENUM_CASE
 
 bool SyncerErrorIsError(SyncerError error) {
   return error != UNSET
       && error != SYNCER_OK
       && error != SERVER_MORE_TO_DOWNLOAD;
 }
 
 }  // namespace syncer