Replace NULL with nullptr or null in webrtc/base/.

webrtc/base/asyncudpsocket.h

Index: webrtc/base/asyncudpsocket.h
diff --git a/webrtc/base/asyncudpsocket.h b/webrtc/base/asyncudpsocket.h
index aa6a9042b479db491f926f22a82e713b7ed6462b..e5535e0273bc1fb0b0d9a750ddb3e66417347089 100644
--- a/webrtc/base/asyncudpsocket.h
+++ b/webrtc/base/asyncudpsocket.h
@@ -23,7 +23,7 @@ namespace rtc {
 class AsyncUDPSocket : public AsyncPacketSocket {
  public:
   // Binds |socket| and creates AsyncUDPSocket for it. Takes ownership
-  // of |socket|. Returns NULL if bind() fails (|socket| is destroyed
+  // of |socket|. Returns null if bind() fails (|socket| is destroyed
   // in that case).
   static AsyncUDPSocket* Create(AsyncSocket* socket,
                                 const SocketAddress& bind_address);