Pref service: Add initial support for pref registration.

services/preferences/public/cpp/pref_registry_serializer.h

Index: services/preferences/public/cpp/pref_registry_serializer.h
diff --git a/services/preferences/public/cpp/pref_registry_serializer.h b/services/preferences/public/cpp/pref_registry_serializer.h
new file mode 100644
index 0000000000000000000000000000000000000000..4e016ce95194260eba919b5037f1ce33e89e705d
--- /dev/null
+++ b/services/preferences/public/cpp/pref_registry_serializer.h
@@ -0,0 +1,18 @@
+// 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.
+
+#ifndef SERVICES_PREFERENCES_PUBLIC_CPP_PREF_REGISTRY_SERIALIZER_H_
+#define SERVICES_PREFERENCES_PUBLIC_CPP_PREF_REGISTRY_SERIALIZER_H_
+
+#include "services/preferences/public/interfaces/preferences.mojom.h"
+
+class PrefRegistry;
+
+namespace prefs {
+
+mojom::PrefRegistryPtr SerializePrefRegistry(PrefRegistry& pref_registry);
+
+}  // namespace prefs
+
+#endif  // SERVICES_PREFERENCES_PUBLIC_CPP_PREF_REGISTRY_SERIALIZER_H_