Replace NULL with nullptr in all C++ files.

webrtc/modules/audio_processing/vad/vad_circular_buffer.cc

 /*
  *  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 15 matching lines @@
 }
 
 void VadCircularBuffer::Reset() {
   is_full_ = false;
   index_ = 0;
   sum_ = 0;
 }
 
 VadCircularBuffer* VadCircularBuffer::Create(int buffer_size) {
   if (buffer_size <= 0)
-    return NULL;
+    return nullptr;
   return new VadCircularBuffer(buffer_size);
 }
 
 double VadCircularBuffer::Oldest() const {
   if (!is_full_)
     return buffer_[0];
   else
     return buffer_[index_];
 }
 
@@ skipping 81 matching lines @@
     }
     for (; index > index_1; index--) {
       if (Set(index, 0.0) < 0)
         return -1;
     }
   }
   return 0;
 }
 
 }  // namespace webrtc