Change preference APIs to take std::string instead of const char*.

base/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 BASE_PREFS_PREF_CHANGE_REGISTRAR_H_
 #define BASE_PREFS_PREF_CHANGE_REGISTRAR_H_
 
 #include <map>
 #include <string>
 
@@ skipping 22 matching lines @@
   void Init(PrefService* service);
 
   // Adds a 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.
   //
   // The second version binds a callback that will receive the path of
   // the preference that is changing as its parameter.
   //
   // Only one observer may be registered per path.
-  void Add(const char* path, const base::Closure& obs);
-  void Add(const char* path, const NamedChangeCallback& obs);
+  void Add(const std::string& path, const base::Closure& obs);
+  void Add(const std::string& path, const NamedChangeCallback& obs);
 
   // Removes the pref observer registered for |path|.
-  void Remove(const char* path);
+  void Remove(const std::string& path);
 
   // 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;
 
   // Check whether |pref| is in the set of preferences being observed.
   bool IsObserved(const std::string& pref);
 
@@ skipping 14 matching lines @@
 
   typedef std::map<std::string, NamedChangeCallback> ObserverMap;
 
   ObserverMap observers_;
   PrefService* service_;
 
   DISALLOW_COPY_AND_ASSIGN(PrefChangeRegistrar);
 };
 
 #endif  // BASE_PREFS_PREF_CHANGE_REGISTRAR_H_