Replace NULL with nullptr in all C++ files.

webrtc/pc/statscollector.cc

Index: webrtc/pc/statscollector.cc
diff --git a/webrtc/pc/statscollector.cc b/webrtc/pc/statscollector.cc
index e91f873824a245ee7284f5a6e154908be627e258..2ee5d1d4e3b698ffcaed3b46a68d2cbfa4dbea59 100644
--- a/webrtc/pc/statscollector.cc
+++ b/webrtc/pc/statscollector.cc
@@ -403,7 +403,7 @@ double StatsCollector::GetTimeNow() {
 // to GetStats.
 void StatsCollector::AddStream(MediaStreamInterface* stream) {
   RTC_DCHECK(pc_->session()->signaling_thread()->IsCurrent());
-  RTC_DCHECK(stream != NULL);
+  RTC_DCHECK(stream != nullptr);
 
   CreateTrackReports<AudioTrackVector>(stream->GetAudioTracks(),
                                        &reports_, track_ids_);
@@ -414,7 +414,7 @@ void StatsCollector::AddStream(MediaStreamInterface* stream) {
 void StatsCollector::AddLocalAudioTrack(AudioTrackInterface* audio_track,
                                         uint32_t ssrc) {
   RTC_DCHECK(pc_->session()->signaling_thread()->IsCurrent());
-  RTC_DCHECK(audio_track != NULL);
+  RTC_DCHECK(audio_track != nullptr);
 #if RTC_DCHECK_IS_ON
   for (const auto& track : local_audio_tracks_)
     RTC_DCHECK(track.first != audio_track || track.second != ssrc);
@@ -435,7 +435,7 @@ void StatsCollector::AddLocalAudioTrack(AudioTrackInterface* audio_track,
 
 void StatsCollector::RemoveLocalAudioTrack(AudioTrackInterface* audio_track,
                                            uint32_t ssrc) {
-  RTC_DCHECK(audio_track != NULL);
+  RTC_DCHECK(audio_track != nullptr);
   local_audio_tracks_.erase(std::remove_if(local_audio_tracks_.begin(),
       local_audio_tracks_.end(),
       [audio_track, ssrc](const LocalAudioTrackVector::value_type& track) {
@@ -446,7 +446,7 @@ void StatsCollector::RemoveLocalAudioTrack(AudioTrackInterface* audio_track,
 void StatsCollector::GetStats(MediaStreamTrackInterface* track,
                               StatsReports* reports) {
   RTC_DCHECK(pc_->session()->signaling_thread()->IsCurrent());
-  RTC_DCHECK(reports != NULL);
+  RTC_DCHECK(reports != nullptr);
   RTC_DCHECK(reports->empty());
 
   rtc::Thread::ScopedDisallowBlockingCalls no_blocking_calls;
@@ -530,9 +530,9 @@ StatsReport* StatsCollector::PrepareReport(
   std::string track_id;
   if (!GetTrackIdBySsrc(ssrc, &track_id, direction)) {
     if (!report) {
-      // The ssrc is not used by any track or existing report, return NULL
+      // The ssrc is not used by any track or existing report, return null
       // in such case to indicate no report is prepared for the ssrc.
-      return NULL;
+      return nullptr;
     }
 
     // The ssrc is not used by any existing track. Keeps the old track id
@@ -564,7 +564,7 @@ bool StatsCollector::IsValidTrack(const std::string& track_id) {
 StatsReport* StatsCollector::AddCertificateReports(
     const rtc::SSLCertificate* cert) {
   RTC_DCHECK(pc_->session()->signaling_thread()->IsCurrent());
-  RTC_DCHECK(cert != NULL);
+  RTC_DCHECK(cert != nullptr);
 
   std::unique_ptr<rtc::SSLCertificateStats> first_stats = cert->GetStats();
   StatsReport* first_report = nullptr;
@@ -909,7 +909,7 @@ void StatsCollector::UpdateStatsFromExistingLocalAudioTracks() {
     StatsReport* report =
         GetReport(StatsReport::kStatsReportTypeSsrc,
                   rtc::ToString<uint32_t>(ssrc), StatsReport::kSend);
-    if (report == NULL) {
+    if (report == nullptr) {
       // This can happen if a local audio track is added to a stream on the
       // fly and the report has not been set up yet. Do nothing in this case.
       LOG(LS_ERROR) << "Stats report does not exist for ssrc " << ssrc;
@@ -930,7 +930,7 @@ void StatsCollector::UpdateStatsFromExistingLocalAudioTracks() {
 void StatsCollector::UpdateReportFromAudioTrack(AudioTrackInterface* track,
                                                 StatsReport* report) {
   RTC_DCHECK(pc_->session()->signaling_thread()->IsCurrent());
-  RTC_DCHECK(track != NULL);
+  RTC_DCHECK(track != nullptr);
 
   // Don't overwrite report values if they're not available.
   int signal_level;