Replace NULL with nullptr in all C++ files.

webrtc/voice_engine/voe_base_impl.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 737 matching lines @@
                                       int accociate_send_channel) {
   rtc::CritScope cs(shared_->crit_sec());
 
   if (!shared_->statistics().Initialized()) {
       shared_->SetLastError(VE_NOT_INITED, kTraceError);
       return -1;
   }
 
   voe::ChannelOwner ch = shared_->channel_manager().GetChannel(channel);
   voe::Channel* channel_ptr = ch.channel();
-  if (channel_ptr == NULL) {
+  if (channel_ptr == nullptr) {
     shared_->SetLastError(VE_CHANNEL_NOT_VALID, kTraceError,
         "AssociateSendChannel() failed to locate channel");
     return -1;
   }
 
   ch = shared_->channel_manager().GetChannel(accociate_send_channel);
   voe::Channel* accociate_send_channel_ptr = ch.channel();
-  if (accociate_send_channel_ptr == NULL) {
+  if (accociate_send_channel_ptr == nullptr) {
     shared_->SetLastError(VE_CHANNEL_NOT_VALID, kTraceError,
         "AssociateSendChannel() failed to locate accociate_send_channel");
     return -1;
   }
 
   channel_ptr->set_associate_send_channel(ch);
   return 0;
 }
 
 }  // namespace webrtc