NULL -> nullptr under athena/

athena/screen_lock/screen_lock_manager_base.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/screen_lock/screen_lock_manager_base.h"
 
 #include "base/logging.h"
 
 namespace athena {
 namespace {
 
-ScreenLockManager* instance = NULL;
+ScreenLockManager* instance = nullptr;
 
 }  // namespace
 
 ScreenLockManagerBase::ScreenLockManagerBase() {
   DCHECK(!instance);
   instance = this;
 }
 
 ScreenLockManagerBase::~ScreenLockManagerBase() {
   DCHECK_EQ(instance, this);
-  instance = NULL;
+  instance = nullptr;
 }
 
 // static
 ScreenLockManager* ScreenLockManager::Get() {
   return instance;
 }
 
 // static
 void ScreenLockManager::Shutdown() {
   if (instance) {
     delete instance;
     DCHECK(!instance);
   }
 }
 
 }  // namespace athena