Replace NULL with nullptr in all C++ files.

webrtc/media/base/mediaengine.cc

 /*
  *  Copyright (c) 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.
  */
 
 #include "webrtc/media/base/mediaengine.h"
 
 #if !defined(DISABLE_MEDIA_ENGINE_FACTORY)
 
 #if defined(HAVE_WEBRTC_VOICE) && defined(HAVE_WEBRTC_VIDEO)
 #include "webrtc/media/engine/webrtcmediaengine.h"
 #endif  // HAVE_WEBRTC_VOICE && HAVE_WEBRTC_VIDEO
 
 namespace cricket {
 
 MediaEngineFactory::MediaEngineCreateFunction
-    MediaEngineFactory::create_function_ = NULL;
+    MediaEngineFactory::create_function_ = nullptr;
 
 MediaEngineFactory::MediaEngineCreateFunction
     MediaEngineFactory::SetCreateFunction(MediaEngineCreateFunction function) {
   MediaEngineCreateFunction old_function = create_function_;
   create_function_ = function;
   return old_function;
 }
 
 };  // namespace cricket
 
 #endif  // DISABLE_MEDIA_ENGINE_FACTORY
 
 namespace cricket {
 
 webrtc::RtpParameters CreateRtpParametersWithOneEncoding() {
   webrtc::RtpParameters parameters;
   webrtc::RtpEncodingParameters encoding;
   parameters.encodings.push_back(encoding);
   return parameters;
 }
 
 };  // namespace cricket