Revamp the MigrateBrowserPrefs and MigrateUserPrefs code.

chrome/browser/chromeos/login/default_pinned_apps_field_trial.h

-// Copyright 2013 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 CHROME_BROWSER_CHROMEOS_LOGIN_DEFAULT_PINNED_APPS_FIELD_TRIAL_H_
-#define CHROME_BROWSER_CHROMEOS_LOGIN_DEFAULT_PINNED_APPS_FIELD_TRIAL_H_
-
-#include <string>
-
-namespace base {
-class ListValue;
-}
-
-class PrefRegistrySimple;
-class PrefService;
-
-namespace chromeos {
-namespace default_pinned_apps_field_trial {
-
-// Registers a local state that keeps track of users in experiment.
-void RegisterPrefs(PrefRegistrySimple* registry);
-
-// Migrate by removing the old local state.
-void MigratePrefs(PrefService* local_state);
-
-}  // namespace default_pinned_apps_field_trial
-}  // namespace chromeos
-
-#endif  // CHROME_BROWSER_CHROMEOS_LOGIN_DEFAULT_PINNED_APPS_FIELD_TRIAL_H_