Add a ClientAction used by SyncRollbackManager to notify PSS that rollback is

sync/internal_api/sync_rollback_manager.h

Index: sync/internal_api/sync_rollback_manager.h
diff --git a/sync/internal_api/sync_rollback_manager.h b/sync/internal_api/sync_rollback_manager.h
index c8b8719b5b0e6abda6168731a3cad4f81b825816..fed4fd403c76136c85f80ebd1236381af4552488 100644
--- a/sync/internal_api/sync_rollback_manager.h
+++ b/sync/internal_api/sync_rollback_manager.h
@@ -47,6 +47,8 @@ class SYNC_EXPORT_PRIVATE SyncRollbackManager : public SyncRollbackManagerBase {
   // Deletes specified entries in local model.
   SyncerError DeleteOnWorkerThread(ModelType type, std::vector<int64> handles);
 
+  void NotifyRollbackDone();
+
   std::map<ModelSafeGroup, scoped_refptr<ModelSafeWorker> > workers_;
 
   SyncManager::ChangeDelegate* change_delegate_;