Pref service: add support for tracked prefs.

services/preferences/public/cpp/tracked_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_PUBLIC_CPP_TRACKED_PERSISTENT_PREF_STORE_FACTORY_H_
+#define SERVICES_PREFERENCES_PUBLIC_CPP_TRACKED_PERSISTENT_PREF_STORE_FACTORY_H_
+
+#include <memory>
+#include <string>
+#include <vector>
+
+#include "base/strings/string16.h"
+#include "components/user_prefs/tracked/pref_hash_filter.h"
+#include "services/preferences/public/interfaces/preferences.mojom.h"
+
+namespace prefs {
+
+PersistentPrefStore* CreateTrackedPersistentPrefStore(
+    scoped_refptr<base::SequencedTaskRunner> io_task_runner,
+    mojom::TrackedPersistentPrefStoreConfigurationPtr config,
+    mojom::TrackedPreferenceValidationDelegate* validation_delegate,
+    const base::Closure& on_reset_on_load);
+
+}  // namespace prefs
+
+#endif  // SERVICES_PREFERENCES_PUBLIC_CPP_TRACKED_PERSISTENT_PREF_STORE_FACTORY_H_