C++11 declares a type safe null pointer

content/common/gpu/gpu_surface_lookup.cc

 // Copyright (c) 2012 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/gpu_surface_lookup.h"
 
 #include "base/logging.h"
 
 namespace content {
 namespace {
-GpuSurfaceLookup* g_instance = NULL;
+GpuSurfaceLookup* g_instance = nullptr;
 } // anonymous namespace
 
 // static
 GpuSurfaceLookup* GpuSurfaceLookup::GetInstance() {
   DCHECK(g_instance);
   return g_instance;
 }
 
 // static
 void GpuSurfaceLookup::InitInstance(GpuSurfaceLookup* lookup) {
   DCHECK(!g_instance || !lookup);
   g_instance = lookup;
 }
 
 }  // namespace content