Don't run WSOLA over always muted channels.

media/renderers/audio_renderer_impl.h

Index: media/renderers/audio_renderer_impl.h
diff --git a/media/renderers/audio_renderer_impl.h b/media/renderers/audio_renderer_impl.h
index b1622cc380deab5be5635f24ece49ef95c1258d3..504a46b6fb4fc1a95bfb36cf1c705df742378f34 100644
--- a/media/renderers/audio_renderer_impl.h
+++ b/media/renderers/audio_renderer_impl.h
@@ -234,6 +234,9 @@ class MEDIA_EXPORT AudioRendererImpl
   // sample rate changes due to implicit AAC configuration change.
   int last_decoded_sample_rate_;
 
+  // Indicates which channels are muted and can be ignored by the algorithm.
+  std::vector<bool> channel_mask_;
+
   // After Initialize() has completed, all variables below must be accessed
   // under |lock_|. ------------------------------------------------------------
   base::Lock lock_;