Revert "Revert 142517 - [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 53195342d1a2604fef56f4de3f490263654801a9..1a2d3f1f5bf8b48b0a2aed1fb901291002dccc6f 100644
--- a/chrome/browser/sync/glue/backend_data_type_configurer.h
+++ b/chrome/browser/sync/glue/backend_data_type_configurer.h
@@ -36,8 +36,8 @@ class BackendDataTypeConfigurer {
       syncer::ModelTypeSet types_to_add,
       syncer::ModelTypeSet types_to_remove,
       NigoriState nigori_state,
-      base::Callback<void(syncer::ModelTypeSet)> ready_task,
-      base::Callback<void()> retry_callback) = 0;
+      const base::Callback<void(syncer::ModelTypeSet)>& ready_task,
+      const base::Callback<void()>& retry_callback) = 0;
 
  protected:
   virtual ~BackendDataTypeConfigurer() {}