Replace NULL with nullptr in all C++ files.

webrtc/p2p/base/relayserver.cc

Index: webrtc/p2p/base/relayserver.cc
diff --git a/webrtc/p2p/base/relayserver.cc b/webrtc/p2p/base/relayserver.cc
index 442f343e024395f9978f3bb76158be12c047a6ae..6bbf452f366be52f5bceb6694d0e858224c3bb41 100644
--- a/webrtc/p2p/base/relayserver.cc
+++ b/webrtc/p2p/base/relayserver.cc
@@ -242,7 +242,7 @@ void RelayServer::OnExternalPacket(
     RelayServerConnection* int_conn =
         ext_conn->binding()->GetInternalConnection(
             ext_conn->addr_pair().source());
-    RTC_DCHECK(int_conn != NULL);
+    RTC_DCHECK(int_conn != nullptr);
     int_conn->Send(bytes, size, ext_conn->addr_pair().source());
     ext_conn->Lock();  // allow outgoing packets
     return;
@@ -290,7 +290,7 @@ void RelayServer::OnExternalPacket(
   // Send this message on the appropriate internal connection.
   RelayServerConnection* int_conn = ext_conn->binding()->GetInternalConnection(
       ext_conn->addr_pair().source());
-  RTC_DCHECK(int_conn != NULL);
+  RTC_DCHECK(int_conn != nullptr);
   int_conn->Send(bytes, size, ext_conn->addr_pair().source());
 }
 
@@ -554,7 +554,7 @@ void RelayServer::AcceptConnection(rtc::AsyncSocket* server_socket) {
   rtc::SocketAddress accept_addr;
   rtc::AsyncSocket* accepted_socket =
       server_socket->Accept(&accept_addr);
-  if (accepted_socket != NULL) {
+  if (accepted_socket != nullptr) {
     // We had someone trying to connect, now check which protocol to
     // use and create a packet socket.
     RTC_DCHECK(server_sockets_[server_socket] == cricket::PROTO_TCP ||