C++11 declares a type safe null pointer

content/common/gpu/client/gpu_memory_buffer_factory_host.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 "content/common/gpu/client/gpu_memory_buffer_factory_host.h"
 
 #include "base/logging.h"
 
 namespace content {
 namespace {
-GpuMemoryBufferFactoryHost* instance = NULL;
+GpuMemoryBufferFactoryHost* instance = nullptr;
 }
 
 // static
 GpuMemoryBufferFactoryHost* GpuMemoryBufferFactoryHost::GetInstance() {
   return instance;
 }
 
 GpuMemoryBufferFactoryHost::GpuMemoryBufferFactoryHost() {
-  DCHECK(instance == NULL);
+  DCHECK(instance == nullptr);
   instance = this;
 }
 
 GpuMemoryBufferFactoryHost::~GpuMemoryBufferFactoryHost() {
-  instance = NULL;
+  instance = nullptr;
 }
 }