Revamp the MigrateBrowserPrefs and MigrateUserPrefs code.

chrome/browser/chromeos/login/default_pinned_apps_field_trial.cc

 // 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.
 
 #include "chrome/browser/chromeos/login/default_pinned_apps_field_trial.h"
 
 #include "base/basictypes.h"
 #include "base/prefs/pref_registry_simple.h"
 #include "base/prefs/pref_service.h"
 
 namespace chromeos {
 namespace default_pinned_apps_field_trial {
 
 namespace {
 
 // Name of a local state pref to store the list of users that participate
 // the experiment.
 const char kExperimentUsers[] = "DefaultPinnedAppsExperimentUsers";
 
 }  // namespace
 
 void RegisterPrefs(PrefRegistrySimple* registry) {
   registry->RegisterListPref(kExperimentUsers);
 }
 
-void MigratePrefs(PrefService* local_state) {

[gab, 2015/02/24 20:55:20]

Delete the rest of this file and its header in fact, it's now only registering
an unused pref :-).

[rkaplow, 2015/02/24 22:41:11]

ah, missed that.  Done

-  // TODO(xiyuan): Remove everything in M34.
-  local_state->ClearPref(kExperimentUsers);
-}
 
 }  // namespace default_pinned_apps_field_trial
 }  // namespace chromeos