Pref service: integrate PersistentPrefStoreImpl with PrefStoreManagerImpl.

services/preferences/public/interfaces/BUILD.gn

 # Copyright 2016 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.
 
 import("//mojo/public/tools/bindings/mojom.gni")
 
 mojom("interfaces") {
   sources = [
     "preferences.mojom",
+    "preferences_configuration.mojom",
     "tracked_preference_validation_delegate.mojom",
   ]
   public_deps = [
     "//mojo/common:common_custom_types",
   ]
 }