Enable sync for the settings from the Extension Settings API.

chrome/browser/extensions/extension_settings_leveldb_storage_unittest.cc

 // Copyright (c) 2011 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.
 
 #include "chrome/browser/extensions/extension_settings_storage_unittest.h"
 
 namespace {
 
 ExtensionSettingsStorage* Param(
-    ExtensionSettings* settings,
-    const std::string& extension_id) {
-  return settings->GetStorageForTesting(
+    const ExtensionSettings& settings, const std::string& extension_id) {
+  return settings.GetStorageForTesting(
       ExtensionSettingsStorage::LEVELDB, false, extension_id);
 }
 
 }  // namespace
 
 INSTANTIATE_TEST_CASE_P(
     ExtensionSettingsLeveldbStorage,
     ExtensionSettingsStorageTest,
     testing::Values(&Param));