Replace NULL with nullptr or null in webrtc/audio/ and common_audio/.

webrtc/common_audio/vad/vad_core.h

 /*
  *  Copyright (c) 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 42 matching lines @@
 
     int init_flag;
 
 } VadInstT;
 
 // Initializes the core VAD component. The default aggressiveness mode is
 // controlled by |kDefaultMode| in vad_core.c.
 //
 // - self [i/o] : Instance that should be initialized
 //
-// returns      : 0 (OK), -1 (NULL pointer in or if the default mode can't be
+// returns      : 0 (OK), -1 (null pointer in or if the default mode can't be
 //                set)
 int WebRtcVad_InitCore(VadInstT* self);
 
 /****************************************************************************
  * WebRtcVad_set_mode_core(...)
  *
  * This function changes the VAD settings
  *
  * Input:
  *      - inst      : VAD instance
@@ skipping 32 matching lines @@
 int WebRtcVad_CalcVad48khz(VadInstT* inst, const int16_t* speech_frame,
                            size_t frame_length);
 int WebRtcVad_CalcVad32khz(VadInstT* inst, const int16_t* speech_frame,
                            size_t frame_length);
 int WebRtcVad_CalcVad16khz(VadInstT* inst, const int16_t* speech_frame,
                            size_t frame_length);
 int WebRtcVad_CalcVad8khz(VadInstT* inst, const int16_t* speech_frame,
                           size_t frame_length);
 
 #endif  // WEBRTC_COMMON_AUDIO_VAD_VAD_CORE_H_