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

base/prefs/pref_notifier_impl.h

 // Copyright (c) 2011 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_NOTIFIER_IMPL_H_
 #define BASE_PREFS_PREF_NOTIFIER_IMPL_H_
 
 #include <list>
 #include <string>
 
@@ skipping 11 matching lines @@
 // The PrefNotifier implementation used by the PrefService.
 class BASE_PREFS_EXPORT PrefNotifierImpl
     : public NON_EXPORTED_BASE(PrefNotifier) {
  public:
   PrefNotifierImpl();
   explicit PrefNotifierImpl(PrefService* pref_service);
   ~PrefNotifierImpl() override;
 
   // If the pref at the given path changes, we call the observer's
   // OnPreferenceChanged method.
-  void AddPrefObserver(const char* path, PrefObserver* observer);
-  void RemovePrefObserver(const char* path, PrefObserver* observer);
+  void AddPrefObserver(const std::string& path, PrefObserver* observer);
+  void RemovePrefObserver(const std::string& path, PrefObserver* observer);
 
   // We run the callback once, when initialization completes. The bool
   // parameter will be set to true for successful initialization,
   // false for unsuccessful.
   void AddInitObserver(base::Callback<void(bool)> observer);
 
   void SetPrefService(PrefService* pref_service);
 
  protected:
   // PrefNotifier overrides.
@@ skipping 20 matching lines @@
 
   PrefObserverMap pref_observers_;
   PrefInitObserverList init_observers_;
 
   base::ThreadChecker thread_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(PrefNotifierImpl);
 };
 
 #endif  // BASE_PREFS_PREF_NOTIFIER_IMPL_H_