Deliver RenderCallbackErrors even when mixer inputs are paused.

media/base/audio_converter.h

Index: media/base/audio_converter.h
diff --git a/media/base/audio_converter.h b/media/base/audio_converter.h
index b921a3a186e47c96d52c1a9090384d6c69d476dc..b12dcb95e7d7193061cc7402b2b97a0d66eb778b 100644
--- a/media/base/audio_converter.h
+++ b/media/base/audio_converter.h
@@ -90,6 +90,8 @@ class MEDIA_EXPORT AudioConverter {
   // to each input's ProvideInput for more data.
   int ChunkSize() const;
 
+  bool empty() const { return transform_inputs_.empty(); }
+
  private:
   // Provides input to the MultiChannelResampler.  Called by the resampler when
   // more data is necessary.