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

webrtc/base/asyncsocket.h

 /*
  *  Copyright 2004 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 24 matching lines @@
                    sigslot::multi_threaded_local> SignalReadEvent;
   // ready to write
   sigslot::signal1<AsyncSocket*,
                    sigslot::multi_threaded_local> SignalWriteEvent;
   sigslot::signal1<AsyncSocket*> SignalConnectEvent;     // connected
   sigslot::signal2<AsyncSocket*, int> SignalCloseEvent;  // closed
 };
 
 class AsyncSocketAdapter : public AsyncSocket, public sigslot::has_slots<> {
  public:
-  // The adapted socket may explicitly be NULL, and later assigned using Attach.
+  // The adapted socket may explicitly be null, and later assigned using Attach.
   // However, subclasses which support detached mode must override any methods
   // that will be called during the detached period (usually GetState()), to
   // avoid dereferencing a null pointer.
   explicit AsyncSocketAdapter(AsyncSocket* socket);
   ~AsyncSocketAdapter() override;
   void Attach(AsyncSocket* socket);
   SocketAddress GetLocalAddress() const override;
   SocketAddress GetRemoteAddress() const override;
   int Bind(const SocketAddress& addr) override;
   int Connect(const SocketAddress& addr) override;
@@ skipping 19 matching lines @@
   virtual void OnReadEvent(AsyncSocket* socket);
   virtual void OnWriteEvent(AsyncSocket* socket);
   virtual void OnCloseEvent(AsyncSocket* socket, int err);
 
   AsyncSocket* socket_;
 };
 
 }  // namespace rtc
 
 #endif  // WEBRTC_BASE_ASYNCSOCKET_H_