Replace NULL with nullptr or null in webrtc/api/.

webrtc/api/mediastreaminterface.h

 /*
  *  Copyright 2012 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 242 matching lines @@
   // Add/Remove a sink that will receive the audio data from the track.
   virtual void AddSink(AudioTrackSinkInterface* sink) = 0;
   virtual void RemoveSink(AudioTrackSinkInterface* sink) = 0;
 
   // Get the signal level from the audio track.
   // Return true on success, otherwise false.
   // TODO(deadbeef): Change the interface to int GetSignalLevel() and pure
   // virtual after it's implemented in chromium.
   virtual bool GetSignalLevel(int* level) { return false; }
 
-  // Get the audio processor used by the audio track. Return NULL if the track
+  // Get the audio processor used by the audio track. Return null if the track
   // does not have any processor.
   // TODO(deadbeef): Make the interface pure virtual.
   virtual rtc::scoped_refptr<AudioProcessorInterface> GetAudioProcessor() {
     return nullptr;
   }
 
  protected:
   virtual ~AudioTrackInterface() {}
 };
 
@@ skipping 27 matching lines @@
   virtual bool RemoveTrack(AudioTrackInterface* track) = 0;
   virtual bool RemoveTrack(VideoTrackInterface* track) = 0;
 
  protected:
   virtual ~MediaStreamInterface() {}
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_API_MEDIASTREAMINTERFACE_H_