[Sync] Refactor sync configuration logic.

chrome/browser/sync/glue/backend_data_type_configurer.h

Index: chrome/browser/sync/glue/backend_data_type_configurer.h
diff --git a/chrome/browser/sync/glue/backend_data_type_configurer.h b/chrome/browser/sync/glue/backend_data_type_configurer.h
index 88dc4d7fe8a2e2155207269cef3da455a2dd07bf..9007d5b2e8d494ff63ced0619f88b724cb0e04c3 100644
--- a/chrome/browser/sync/glue/backend_data_type_configurer.h
+++ b/chrome/browser/sync/glue/backend_data_type_configurer.h
@@ -33,12 +33,12 @@ class BackendDataTypeConfigurer {
   // SyncBackendHost calls ConfigureDataTypes on itself to configure
   // Nigori.
   virtual void ConfigureDataTypes(
-      sync_api::ConfigureReason reason,
-      syncable::ModelTypeSet types_to_add,
-      syncable::ModelTypeSet types_to_remove,
+      const sync_api::ConfigureReason& reason,
+      const syncable::ModelTypeSet& types_to_add,
+      const syncable::ModelTypeSet& types_to_remove,
       NigoriState nigori_state,
-      base::Callback<void(syncable::ModelTypeSet)> ready_task,
-      base::Callback<void()> retry_callback) = 0;
+      const base::Callback<void(syncable::ModelTypeSet)>& ready_task,
+      const base::Callback<void()>& retry_callback) = 0;
 
  protected:
   virtual ~BackendDataTypeConfigurer() {}