Replace NULL with nullptr in all C++ files.

webrtc/audio/audio_receive_stream.cc

Index: webrtc/audio/audio_receive_stream.cc
diff --git a/webrtc/audio/audio_receive_stream.cc b/webrtc/audio/audio_receive_stream.cc
index 05d6edfa4c1fccd33b953ec2e38c3c456eefcb83..ccf97d549e27de34ac2605d58224293eb685b2e9 100644
--- a/webrtc/audio/audio_receive_stream.cc
+++ b/webrtc/audio/audio_receive_stream.cc
@@ -51,7 +51,7 @@ std::string AudioReceiveStream::Config::ToString() const {
   std::stringstream ss;
   ss << "{rtp: " << rtp.ToString();
   ss << ", rtcp_send_transport: "
-     << (rtcp_send_transport ? "(Transport)" : "nullptr");
+     << (rtcp_send_transport ? "(Transport)" : "null");

[tommi, 2017/02/11 09:55:34]

in cases like these, I think we should not change to nullptr.  The reason is
that nullptr to me means C++ whereas this is log related and representation of
nullptr values in JS and upper level languages is typically 'null'.

[Taylor Brandstetter, 2017/02/11 17:48:56]

I agree; the script I wrote will use "null" in strings and comments, and
"nullptr" in actual code.

   ss << ", voe_channel_id: " << voe_channel_id;
   if (!sync_group.empty()) {
     ss << ", sync_group: " << sync_group;