Pref service: integrate PersistentPrefStoreImpl with PrefStoreManagerImpl.

services/preferences/public/interfaces/preferences_configuration.mojom

Index: services/preferences/public/interfaces/preferences_configuration.mojom
diff --git a/services/preferences/public/interfaces/preferences_configuration.mojom b/services/preferences/public/interfaces/preferences_configuration.mojom
new file mode 100644
index 0000000000000000000000000000000000000000..3ddd8234cb02a8b30b0960e423cfa8bccaf0fb33
--- /dev/null
+++ b/services/preferences/public/interfaces/preferences_configuration.mojom
@@ -0,0 +1,15 @@
+// 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.
+
+module prefs.mojom;
+
+import "mojo/common/file_path.mojom";
+
+union PersistentPrefStoreConfiguration {
+  SimplePersistentPrefStoreConfiguration simple_configuration;
+};
+
+struct SimplePersistentPrefStoreConfiguration {
+  mojo.common.mojom.FilePath pref_filename;
+};