[chromecast] Deletes dead code to track MediaPipelineBackend.

chromecast/media/cma/pipeline/media_pipeline_impl.h

Index: chromecast/media/cma/pipeline/media_pipeline_impl.h
diff --git a/chromecast/media/cma/pipeline/media_pipeline_impl.h b/chromecast/media/cma/pipeline/media_pipeline_impl.h
index 87fec0e1bce25ea370ceb3d40a30a96089434ae6..1e5959c117f2b4387c2b543cdf676395fb932407 100644
--- a/chromecast/media/cma/pipeline/media_pipeline_impl.h
+++ b/chromecast/media/cma/pipeline/media_pipeline_impl.h
@@ -99,10 +99,12 @@ class MediaPipelineImpl {
   // Cached here because CMA pipeline backend does not support rate == 0,
   // which is emulated by pausing the backend.
   float playback_rate_;
+
+  // Since av pipeline still need to access device components in their
+  // destructor, it's important to delete them first.
   std::unique_ptr<MediaPipelineBackend> media_pipeline_backend_;
   std::unique_ptr<AudioDecoderSoftwareWrapper> audio_decoder_;
   MediaPipelineBackend::VideoDecoder* video_decoder_;
-
   std::unique_ptr<AudioPipelineImpl> audio_pipeline_;
   std::unique_ptr<VideoPipelineImpl> video_pipeline_;
   std::unique_ptr<FlushTask> pending_flush_task_;