Pref service: Merge PrefStoreConnector interfaces.

services/preferences/public/cpp/pref_service_factory.h

 // Copyright 2017 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.
 
 // This provides a way for any service to connect to the pref service to access
 // the application's current preferences.
 
 // Access is provided through a synchronous interface, exposed using the
 // |PrefService| class.
 
@@ skipping 18 matching lines @@
 // failure.
 using ConnectCallback = base::Callback<void(std::unique_ptr<::PrefService>)>;
 
 // Create a |PrefService| object acting as a client library for the pref
 // service, by connecting to the service using |connector|. Connecting is
 // asynchronous and |callback| will be called when it has been established. All
 // preferences that will be accessed need to be registered in |pref_registry|
 // first.
 void ConnectToPrefService(service_manager::Connector* connector,
                           scoped_refptr<PrefRegistry> pref_registry,
-                          const ConnectCallback& callback);
+                          ConnectCallback callback);
 
 }  // namespace prefs
 
 #endif  // SERVICES_PREFERENCES_PUBLIC_CPP_PREF_SERVICE_FACTORY_H_