NULL -> nullptr under athena/

athena/activity/activity_factory.cc

 // Copyright 2014 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 "athena/activity/public/activity_factory.h"
 
 #include "base/logging.h"
 
 namespace athena {
 
 namespace {
 
-ActivityFactory* instance = NULL;
-
+ActivityFactory* instance = nullptr;
 }
 
 // static
 void ActivityFactory::RegisterActivityFactory(ActivityFactory* factory) {
   DCHECK(!instance);
   instance = factory;
 }
 
 // static
 ActivityFactory* ActivityFactory::Get() {
   DCHECK(instance);
   return instance;
 }
 
 // static
 void ActivityFactory::Shutdown() {
   DCHECK(instance);
   delete instance;
-  instance = NULL;
+  instance = nullptr;
 }
 
 }  // namespace athena