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

remoting/host/audio_capturer_linux.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/host/audio_capturer_linux.h"
 
 #include "base/files/file_path.h"
 #include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "remoting/proto/audio.pb.h"
@@ skipping 65 matching lines @@
 }
 
 bool AudioCapturer::IsSupported() {
   return g_pulseaudio_pipe_sink_reader.Get().get() != NULL;
 }
 
 scoped_ptr<AudioCapturer> AudioCapturer::Create() {
   scoped_refptr<AudioPipeReader> reader =
       g_pulseaudio_pipe_sink_reader.Get();
   if (!reader.get())
-    return scoped_ptr<AudioCapturer>();
+    return nullptr;
   return scoped_ptr<AudioCapturer>(new AudioCapturerLinux(reader));
 }
 
 }  // namespace remoting