MediaStream audio sourcing: Bypass audio processing for non-WebRTC cases.

media/base/audio_fifo.h

Index: media/base/audio_fifo.h
diff --git a/media/base/audio_fifo.h b/media/base/audio_fifo.h
index 213a61e9b2abb85a71ebd58df471ed974297419c..25dabf7e15af731fb55e6329ade87a3dcc86fdf3 100644
--- a/media/base/audio_fifo.h
+++ b/media/base/audio_fifo.h
@@ -16,6 +16,9 @@ namespace media {
 // can not be extended dynamically.  The allocated memory is utilized as a
 // ring buffer.
 // This class is thread-unsafe.
+//
+// NOTE: Consider using the more-efficient and easier-to-use AudioRechunker
+// instead of this FIFO implementation.
 class MEDIA_EXPORT AudioFifo {
  public:
   // Creates a new AudioFifo and allocates |channels| of length |frames|.