Replace NULL with nullptr in all C++ files.

webrtc/modules/audio_coding/neteq/tools/rtp_file_source.cc

Index: webrtc/modules/audio_coding/neteq/tools/rtp_file_source.cc
diff --git a/webrtc/modules/audio_coding/neteq/tools/rtp_file_source.cc b/webrtc/modules/audio_coding/neteq/tools/rtp_file_source.cc
index 9ca48e9ea5be0caa5657474e0fff3745bc56ba66..052436efbb6b8a9d031b21f597ef82315c6d8f41 100644
--- a/webrtc/modules/audio_coding/neteq/tools/rtp_file_source.cc
+++ b/webrtc/modules/audio_coding/neteq/tools/rtp_file_source.cc
@@ -59,7 +59,7 @@ std::unique_ptr<Packet> RtpFileSource::NextPacket() {
   while (true) {
     RtpPacket temp_packet;
     if (!rtp_reader_->NextPacket(&temp_packet)) {
-      return NULL;
+      return nullptr;
     }
     if (temp_packet.original_length == 0) {
       // May be an RTCP packet.
@@ -73,7 +73,7 @@ std::unique_ptr<Packet> RtpFileSource::NextPacket() {
         temp_packet.original_length, temp_packet.time_ms, *parser_.get()));
     if (!packet->valid_header()) {
       assert(false);
-      return NULL;
+      return nullptr;
     }
     if (filter_.test(packet->header().payloadType) ||
         (use_ssrc_filter_ && packet->header().ssrc != ssrc_)) {