Revamp the MigrateBrowserPrefs and MigrateUserPrefs code.

chrome/browser/ui/prefs/prefs_tab_helper.cc

 // Copyright (c) 2012 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/ui/prefs/prefs_tab_helper.h"
 
 #include <set>
 #include <string>
 
 #include "base/memory/singleton.h"
@@ skipping 489 matching lines @@
 PrefsTabHelper::~PrefsTabHelper() {
   PrefWatcher::Get(profile_)->UnregisterHelper(this);
 }
 
 // static
 void PrefsTabHelper::InitIncognitoUserPrefStore(
     OverlayUserPrefStore* pref_store) {
   // List of keys that cannot be changed in the user prefs file by the incognito
   // profile.  All preferences that store information about the browsing history
   // or behavior of the user should have this property.
-  pref_store->RegisterOverlayPref(prefs::kBrowserWindowPlacement);
   pref_store->RegisterOverlayPref(prefs::kSaveFileDefaultDirectory);
 #if defined(OS_ANDROID) || defined(OS_IOS)
   pref_store->RegisterOverlayPref(prefs::kProxy);
 #endif  // defined(OS_ANDROID) || defined(OS_IOS)
 }
 
 // static
 void PrefsTabHelper::RegisterProfilePrefs(
     user_prefs::PrefRegistrySyncable* registry) {
   WebPreferences pref_defaults;
@@ skipping 215 matching lines @@
   }
 }
 
 void PrefsTabHelper::OnWebPrefChanged(const std::string& pref_name) {
 #if !defined(OS_ANDROID)
   OnFontFamilyPrefChanged(pref_name);
 #endif
 
   web_contents_->GetRenderViewHost()->OnWebkitPreferencesChanged();
 }