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

base/prefs/pref_member_unittest.cc

 // 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.
 
 #include "base/prefs/pref_member.h"
 
 #include "base/bind.h"
 #include "base/message_loop/message_loop.h"
 #include "base/prefs/pref_registry_simple.h"
 #include "base/prefs/testing_pref_service.h"
@@ skipping 17 matching lines @@
   registry->RegisterListPref(kStringListPref, new base::ListValue());
 }
 
 class GetPrefValueHelper
     : public base::RefCountedThreadSafe<GetPrefValueHelper> {
  public:
   GetPrefValueHelper() : value_(false), pref_thread_("pref thread") {
     pref_thread_.Start();
   }
 
-  void Init(const char* pref_name, PrefService* prefs) {
+  void Init(const std::string& pref_name, PrefService* prefs) {
     pref_.Init(pref_name, prefs);
     pref_.MoveToThread(pref_thread_.message_loop_proxy());
   }
 
   void Destroy() {
     pref_.Destroy();
   }
 
   void FetchValue() {
     base::WaitableEvent event(true, false);
@@ skipping 263 matching lines @@
   helper->FetchValue();
   EXPECT_TRUE(helper->value());
 
   helper->Destroy();
 
   helper->FetchValue();
   EXPECT_TRUE(helper->value());
 
   helper->StopThread();
 }