Cleanup usage of scoped_ptr<> in remoting for C++11

remoting/codec/audio_decoder.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "remoting/codec/audio_decoder.h"
 
 #include "base/logging.h"
 #include "remoting/codec/audio_decoder_opus.h"
 #include "remoting/codec/audio_decoder_verbatim.h"
 #include "remoting/protocol/session_config.h"
 
 namespace remoting {
 
 scoped_ptr<AudioDecoder> AudioDecoder::CreateAudioDecoder(
     const protocol::SessionConfig& config) {
   const protocol::ChannelConfig& audio_config = config.audio_config();
 
   if (audio_config.codec == protocol::ChannelConfig::CODEC_VERBATIM) {
     return scoped_ptr<AudioDecoder>(new AudioDecoderVerbatim());
   } else if (audio_config.codec == protocol::ChannelConfig::CODEC_OPUS) {
     return scoped_ptr<AudioDecoder>(new AudioDecoderOpus());
   }
 
   NOTIMPLEMENTED();
-  return scoped_ptr<AudioDecoder>();
+  return nullptr;
 }
 
 }  // namespace remoting