NULL -> nullptr under athena/

athena/test/base/activity_lifetime_tracker.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/test/base/activity_lifetime_tracker.h"
 
 #include "athena/activity/public/activity_manager.h"
 
 namespace athena {
 
-ActivityLifetimeTracker::ActivityLifetimeTracker() : new_activity_(NULL),
-                                                     deleted_activity_(NULL) {
+ActivityLifetimeTracker::ActivityLifetimeTracker()
+    : new_activity_(nullptr), deleted_activity_(nullptr) {
   ActivityManager::Get()->AddObserver(this);
 }
 
 ActivityLifetimeTracker::~ActivityLifetimeTracker() {
   ActivityManager::Get()->RemoveObserver(this);
 }
 
 void ActivityLifetimeTracker::OnActivityStarted(Activity* activity) {
   new_activity_ = activity;
 }
 
 void ActivityLifetimeTracker::OnActivityEnding(Activity* activity) {
   deleted_activity_ = activity;
 }
 
 Activity* ActivityLifetimeTracker::GetNewActivityAndReset() {
   Activity* activity = new_activity_;
-  new_activity_ = NULL;
+  new_activity_ = nullptr;
   return activity;
 }
 
 void* ActivityLifetimeTracker::GetDeletedActivityAndReset() {
   void* activity = deleted_activity_;
-  deleted_activity_ = NULL;
+  deleted_activity_ = nullptr;
   return activity;
 }
 
 }  // namespace athena