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

base/prefs/mock_pref_change_callback.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_MOCK_PREF_CHANGE_CALLBACK_H_
 #define BASE_PREFS_MOCK_PREF_CHANGE_CALLBACK_H_
 
 #include <string>
 
 #include "base/prefs/pref_change_registrar.h"
 #include "base/prefs/pref_service.h"
 #include "testing/gmock/include/gmock/gmock.h"
 
 using testing::Pointee;
 using testing::Property;
 using testing::Truly;
 
 // Matcher that checks whether the current value of the preference named
 // |pref_name| in |prefs| matches |value|. If |value| is NULL, the matcher
 // checks that the value is not set.
 MATCHER_P3(PrefValueMatches, prefs, pref_name, value, "") {
-  const PrefService::Preference* pref =
-      prefs->FindPreference(pref_name.c_str());
+  const PrefService::Preference* pref = prefs->FindPreference(pref_name);
   if (!pref)
     return false;
 
   const base::Value* actual_value = pref->GetValue();
   if (!actual_value)
     return value == NULL;
   if (!value)
     return actual_value == NULL;
   return value->Equals(actual_value);
 }
 
 // A mock for testing preference notifications and easy setup of expectations.
 class MockPrefChangeCallback {
  public:
   explicit MockPrefChangeCallback(PrefService* prefs);
   virtual ~MockPrefChangeCallback();
 
   PrefChangeRegistrar::NamedChangeCallback GetCallback();
 
   MOCK_METHOD1(OnPreferenceChanged, void(const std::string&));
 
   void Expect(const std::string& pref_name,
               const base::Value* value);
 
  private:
   PrefService* prefs_;
 };
 
 #endif  // BASE_PREFS_MOCK_PREF_CHANGE_CALLBACK_H_