Replace NULL with nullptr in all C++ files.

webrtc/media/engine/webrtcvoiceengine.cc

Index: webrtc/media/engine/webrtcvoiceengine.cc
diff --git a/webrtc/media/engine/webrtcvoiceengine.cc b/webrtc/media/engine/webrtcvoiceengine.cc
index f96c8e741e04ad94075ad69add97fab351230e01..af3d3525c96197829c550b67012d32f85d97ff4f 100644
--- a/webrtc/media/engine/webrtcvoiceengine.cc
+++ b/webrtc/media/engine/webrtcvoiceengine.cc
@@ -158,7 +158,7 @@ bool FindCodec(const std::vector<AudioCodec>& codecs,
                AudioCodec* found_codec) {
   for (const AudioCodec& c : codecs) {
     if (c.Matches(codec)) {
-      if (found_codec != NULL) {
+      if (found_codec != nullptr) {
         *found_codec = c;
       }
       return true;
@@ -2661,7 +2661,7 @@ void WebRtcVoiceMediaChannel::SetRawAudioSink(
     std::unique_ptr<webrtc::AudioSinkInterface> sink) {
   RTC_DCHECK(worker_thread_checker_.CalledOnValidThread());
   LOG(LS_VERBOSE) << "WebRtcVoiceMediaChannel::SetRawAudioSink: ssrc:" << ssrc
-                  << " " << (sink ? "(ptr)" : "NULL");
+                  << " " << (sink ? "(ptr)" : "null");
   if (ssrc == 0) {
     if (default_recv_ssrc_ != -1) {
       std::unique_ptr<webrtc::AudioSinkInterface> proxy_sink(