Remove dependency of PrefSyncableService on PrefsTabHelper.

chrome/browser/prefs/pref_service_syncable_util.h

 // Copyright 2015 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_PREFS_PREF_SERVICE_SYNCABLE_UTIL_H_
 #define CHROME_BROWSER_PREFS_PREF_SERVICE_SYNCABLE_UTIL_H_
 
 class PrefServiceSyncable;
+class PrefStore;
 class Profile;
 
 // PrefServiceSyncable is a PrefService with added integration for
 // sync, and knowledge of how to create an incognito
 // PrefService. For code that does not need to know about the sync
 // integration, you should use only the plain PrefService type.
 //
 // For this reason, Profile does not expose an accessor for the
 // PrefServiceSyncable type. Instead, you can use the utilities
 // below to retrieve the PrefServiceSyncable (or its incognito
 // version) from a Profile.
 PrefServiceSyncable* PrefServiceSyncableFromProfile(Profile* profile);
 PrefServiceSyncable* PrefServiceSyncableIncognitoFromProfile(Profile* profile);
 
+// Creates an incognito copy of |pref_service| that shares most prefs but uses
+// a fresh non-persistent overlay for the user pref store and an individual
+// extension pref store (to cache the effective extension prefs for incognito
+// windows).
+PrefServiceSyncable* CreateIncognitoPrefServiceSyncable(
+    PrefServiceSyncable* pref_service,
+    PrefStore* incognito_extension_pref_store);
+
 #endif  // CHROME_BROWSER_PREFS_PREF_SERVICE_SYNCABLE_UTIL_H_