replace NULL->nullptr in src/remoting.

remoting/host/audio_capturer.h

 // 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.
 
 #ifndef REMOTING_HOST_AUDIO_CAPTURER_H_
 #define REMOTING_HOST_AUDIO_CAPTURER_H_
 
 #include "base/callback.h"
 #include "base/memory/scoped_ptr.h"
 
 namespace remoting {
 
 class AudioPacket;
 
 class AudioCapturer {
  public:
   typedef base::Callback<void(scoped_ptr<AudioPacket> packet)>
       PacketCapturedCallback;
 
   virtual ~AudioCapturer() {}
 
   // Returns true if audio capturing is supported on this platform. If this
-  // returns true, then Create() must not return NULL.
+  // returns true, then Create() must not return nullptr.
   static bool IsSupported();
   static scoped_ptr<AudioCapturer> Create();
 
   // Capturers should sample at a 44.1 or 48 kHz sampling rate, in uncompressed
   // PCM stereo format. Capturers may choose the number of frames per packet.
   // Returns true on success.
   virtual bool Start(const PacketCapturedCallback& callback) = 0;
   // Stops the audio capturer, and frees the OS-specific audio capture
   // resources.
   virtual void Stop() = 0;
   // Returns true if the audio capturer is running.
   virtual bool IsStarted() = 0;
 
   static bool IsValidSampleRate(int sample_rate);
 };
 
 }  // namespace remoting
 
 #endif  // REMOTING_HOST_AUDIO_CAPTURER_H_