Watch the preferences for changes per profile instead of per tab.

chrome/browser/ui/prefs/prefs_tab_helper.h

 // 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.
 
 #ifndef CHROME_BROWSER_UI_PREFS_PREFS_TAB_HELPER_H_
 #define CHROME_BROWSER_UI_PREFS_PREFS_TAB_HELPER_H_
 
 #include "base/callback_list.h"
 #include "base/compiler_specific.h"
 #include "base/memory/weak_ptr.h"
-#include "base/prefs/pref_change_registrar.h"
 #include "chrome/browser/ui/zoom/chrome_zoom_level_prefs.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 #include "content/public/browser/web_contents_user_data.h"
 
 class OverlayUserPrefStore;
 class PrefService;
 class Profile;
 
 namespace content {
 class WebContents;
 }
 
 namespace user_prefs {
 class PrefRegistrySyncable;
 }
 
 // Per-tab class to handle user preferences.
 class PrefsTabHelper : public content::NotificationObserver,
                        public content::WebContentsUserData<PrefsTabHelper> {
  public:
   ~PrefsTabHelper() override;
 
   static void InitIncognitoUserPrefStore(OverlayUserPrefStore* pref_store);
   static void RegisterProfilePrefs(user_prefs::PrefRegistrySyncable* registry);
+  static void GetServiceInstance();
 
  protected:
   // Update the RenderView's WebPreferences. Exposed as protected for testing.
   virtual void UpdateWebPreferences();
 
  private:
   explicit PrefsTabHelper(content::WebContents* contents);
   friend class content::WebContentsUserData<PrefsTabHelper>;
+  friend class PrefWatcher;

[Bernhard Bauer, 2015/01/28 23:35:52]

Can we move PrefWatcher into this class? Then we wouldn't need to friend it, and
we would avoid potential naming collisions due to PrefWatcher being in the
global namespace.

 
   // content::NotificationObserver overrides:
   void Observe(int type,
                const content::NotificationSource& source,
                const content::NotificationDetails& details) override;
 
   // Update the WebContents's RendererPreferences.
   void UpdateRendererPreferences();
 
-  Profile* GetProfile();
-
   void OnFontFamilyPrefChanged(const std::string& pref_name);
   void OnWebPrefChanged(const std::string& pref_name);
 
   content::WebContents* web_contents_;
+  Profile* profile_;
   content::NotificationRegistrar registrar_;
-  PrefChangeRegistrar pref_change_registrar_;
   scoped_ptr<base::CallbackList<void(void)>::Subscription>
       style_sheet_subscription_;
   scoped_ptr<chrome::ChromeZoomLevelPrefs::DefaultZoomLevelSubscription>
       default_zoom_level_subscription_;
   base::WeakPtrFactory<PrefsTabHelper> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(PrefsTabHelper);
 };
 
 #endif  // CHROME_BROWSER_UI_PREFS_PREFS_TAB_HELPER_H_