Use PrefChangeRegistrar everywhere

chrome/browser/prefs/pref_change_registrar.h

 // Copyright (c) 2010 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_CHANGE_REGISTRAR_H_
 #define CHROME_BROWSER_PREFS_PREF_CHANGE_REGISTRAR_H_
 #pragma once
 
 #include <set>
 #include <string>
 
 #include "base/basictypes.h"
 
 class PrefService;
 class NotificationObserver;
 
 // Automatically manages the registration of one or more pref change observers
 // with a PrefStore. Functions much like NotificationRegistrar, but specifically
 // manages observers of preference changes. When the Registrar is destroyed,
 // all registered observers are automatically unregistered with the PrefStore.
 class PrefChangeRegistrar {
  public:
   PrefChangeRegistrar();
   virtual ~PrefChangeRegistrar();
 
-  // Must be called before adding or removing observers.
+  // Must be called before adding or removing observers. Can be called more
+  // than once as long as the value of |service| doesn't change.
   void Init(PrefService* service);
 
   // Adds an pref observer for the specified pref |path| and |obs| observer
   // object. All registered observers will be automatically unregistered
   // when the registrar's destructor is called unless the observer has been
   // explicitly removed by a call to Remove beforehand.
   void Add(const char* path,
            NotificationObserver* obs);
 
   // Removes a preference observer that has previously been added with a call to
   // Add.
   void Remove(const char* path,
               NotificationObserver* obs);
 
+  // Removes all observers that have been previously added with a call to Add.
+  void RemoveAll();
+
+  // Returns true if no pref observers are registered.
+  bool IsEmpty() const;
+
  private:
   typedef std::pair<std::string, NotificationObserver*> ObserverRegistration;
 
   std::set<ObserverRegistration> observers_;
   PrefService* service_;
 
   DISALLOW_COPY_AND_ASSIGN(PrefChangeRegistrar);
 };
 
 #endif  // CHROME_BROWSER_PREFS_PREF_CHANGE_REGISTRAR_H_