Add a mojo bridge for PersistentPrefStore.

services/preferences/public/cpp/preferences_struct_traits.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_PREFERENCES_STRUCT_TRAITS_H_
+#define SERVICES_PREFERENCES_PUBLIC_CPP_PREFERENCES_STRUCT_TRAITS_H_
+
+#include "components/prefs/persistent_pref_store.h"
+#include "mojo/public/cpp/bindings/enum_traits.h"
+#include "services/preferences/public/interfaces/preferences.mojom-shared.h"
+
+namespace mojo {
+
+template <>
+struct EnumTraits<::prefs::mojom::PersistentPrefStoreConnector_ReadError,
+                  ::PersistentPrefStore::PrefReadError> {
+  static prefs::mojom::PersistentPrefStoreConnector_ReadError ToMojom(
+      PersistentPrefStore::PrefReadError input);
+
+  static bool FromMojom(
+      prefs::mojom::PersistentPrefStoreConnector_ReadError input,
+      PersistentPrefStore::PrefReadError* output);
+};
+
+}  // namespace mojo
+
+#endif  // SERVICES_PREFERENCES_PUBLIC_CPP_PREFERENCES_STRUCT_TRAITS_H_