Convert //chromecast from scoped_ptr to std::unique_ptr

chromecast/media/audio/cast_audio_manager.cc

Index: chromecast/media/audio/cast_audio_manager.cc
diff --git a/chromecast/media/audio/cast_audio_manager.cc b/chromecast/media/audio/cast_audio_manager.cc
index 1321e90acab6c0e52620f308ffb9f49602631301..b098b56c4c5fd8154db604ba3af4c256dd340071 100644
--- a/chromecast/media/audio/cast_audio_manager.cc
+++ b/chromecast/media/audio/cast_audio_manager.cc
@@ -61,7 +61,8 @@ void CastAudioManager::GetAudioInputDeviceNames(
       ::media::CHANNEL_LAYOUT_STEREO, 48000, 16, 1024);
 }
 
-scoped_ptr<MediaPipelineBackend> CastAudioManager::CreateMediaPipelineBackend(
+std::unique_ptr<MediaPipelineBackend>
+CastAudioManager::CreateMediaPipelineBackend(
     const MediaPipelineDeviceParams& params) {
   return backend_manager_->CreateMediaPipelineBackend(params);
 }