Replace NULL with nullptr in all C++ files.

webrtc/pc/quicdatachannel.cc

 /*
  *  Copyright 2016 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 207 matching lines @@
     cricket::ReliableQuicStream* stream = kv.second;
     stream->Close();
   }
 }
 
 bool QuicDataChannel::SetTransportChannel(
     cricket::QuicTransportChannel* channel) {
   RTC_DCHECK(signaling_thread_->IsCurrent());
 
   if (!channel) {
-    LOG(LS_ERROR) << "|channel| is NULL. Cannot set transport channel.";
+    LOG(LS_ERROR) << "|channel| is null. Cannot set transport channel.";
     return false;
   }
   if (quic_transport_channel_) {
     if (channel == quic_transport_channel_) {
       LOG(LS_WARNING) << "Ignoring duplicate transport channel.";
       return true;
     }
     LOG(LS_ERROR) << "|channel| does not match existing transport channel.";
     return false;
   }
@@ skipping 148 matching lines @@
 
 size_t QuicDataChannel::GetNumWriteBlockedStreams() const {
   return write_blocked_quic_streams_.size();
 }
 
 size_t QuicDataChannel::GetNumIncomingStreams() const {
   return incoming_quic_messages_.size();
 }
 
 }  // namespace webrtc