Replace NULL with nullptr in all C++ files.

webrtc/modules/rtp_rtcp/source/rtp_utility.cc

Index: webrtc/modules/rtp_rtcp/source/rtp_utility.cc
diff --git a/webrtc/modules/rtp_rtcp/source/rtp_utility.cc b/webrtc/modules/rtp_rtcp/source/rtp_utility.cc
index def431f1709499993bac608a993aa0c49e33bc1b..08d23090bd009ac198b603d1f49ed2e63b8e3aba 100644
--- a/webrtc/modules/rtp_rtcp/source/rtp_utility.cc
+++ b/webrtc/modules/rtp_rtcp/source/rtp_utility.cc
@@ -71,8 +71,7 @@ size_t Word32Align(size_t size) {
 RtpHeaderParser::RtpHeaderParser(const uint8_t* rtpData,
                                  const size_t rtpDataLength)
     : _ptrRTPDataBegin(rtpData),
-      _ptrRTPDataEnd(rtpData ? (rtpData + rtpDataLength) : NULL) {
-}
+      _ptrRTPDataEnd(rtpData ? (rtpData + rtpDataLength) : nullptr) {}
 
 RtpHeaderParser::~RtpHeaderParser() {
 }
@@ -151,7 +150,7 @@ bool RtpHeaderParser::RTCP() const {
 }
 
 bool RtpHeaderParser::ParseRtcp(RTPHeader* header) const {
-  assert(header != NULL);
+  assert(header != nullptr);
 
   const ptrdiff_t length = _ptrRTPDataEnd - _ptrRTPDataBegin;
   if (length < kRtcpMinParseLength) {