Replace NULL with nullptr in all C++ files.

webrtc/modules/rtp_rtcp/source/rtp_receiver_video.cc

Index: webrtc/modules/rtp_rtcp/source/rtp_receiver_video.cc
diff --git a/webrtc/modules/rtp_rtcp/source/rtp_receiver_video.cc b/webrtc/modules/rtp_rtcp/source/rtp_receiver_video.cc
index d6c5e5c29b6ac4667f80681c0df5322d645747a1..622806c0cff325c713386cab659abcecd0627014 100644
--- a/webrtc/modules/rtp_rtcp/source/rtp_receiver_video.cc
+++ b/webrtc/modules/rtp_rtcp/source/rtp_receiver_video.cc
@@ -65,9 +65,10 @@ int32_t RTPReceiverVideo::ParseRtpPacket(WebRtcRTPHeader* rtp_header,
   const size_t payload_data_length =
       payload_length - rtp_header->header.paddingLength;
 
-  if (payload == NULL || payload_data_length == 0) {
-    return data_callback_->OnReceivedPayloadData(NULL, 0, rtp_header) == 0 ? 0
-                                                                           : -1;
+  if (payload == nullptr || payload_data_length == 0) {
+    return data_callback_->OnReceivedPayloadData(nullptr, 0, rtp_header) == 0
+               ? 0
+               : -1;
   }
 
   if (first_packet_received_()) {
@@ -77,7 +78,7 @@ int32_t RTPReceiverVideo::ParseRtpPacket(WebRtcRTPHeader* rtp_header,
   // We are not allowed to hold a critical section when calling below functions.
   std::unique_ptr<RtpDepacketizer> depacketizer(
       RtpDepacketizer::Create(rtp_header->type.Video.codec));
-  if (depacketizer.get() == NULL) {
+  if (depacketizer.get() == nullptr) {
     LOG(LS_ERROR) << "Failed to create depacketizer.";
     return -1;
   }