Pref service: integrate PersistentPrefStoreImpl with PrefStoreManagerImpl.

services/preferences/persistent_pref_store_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.
+
+#ifndef SERVICES_PREFERENCES_PERSISTENT_PREF_STORE_FACTORY_H_
+#define SERVICES_PREFERENCES_PERSISTENT_PREF_STORE_FACTORY_H_
+
+#include <memory>
+
+#include "services/preferences/public/interfaces/preferences.mojom.h"
+
+namespace base {
+class SequencedWorkerPool;
+}
+
+namespace prefs {
+class PersistentPrefStoreImpl;
+
+// Create a new mojom::PersistentPrefStore impl that runs on |worker_pool|
+// configured by |configuration|.
+std::unique_ptr<PersistentPrefStoreImpl> CreatePersistentPrefStore(
+    mojom::PersistentPrefStoreConfigurationPtr configuration,
+    base::SequencedWorkerPool* worker_pool);
+
+}  // namespace prefs
+
+#endif  // SERVICES_PREFERENCES_PERSISTENT_PREF_STORE_FACTORY_H_