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

media/base/audio_block_fifo.h

Index: media/base/audio_block_fifo.h
diff --git a/media/base/audio_block_fifo.h b/media/base/audio_block_fifo.h
index a90a3dfe65661a3b089f517703c53d9de6c18f78..8da932dffa6bc7a87fb682e08fb67c9623835ef0 100644
--- a/media/base/audio_block_fifo.h
+++ b/media/base/audio_block_fifo.h
@@ -17,6 +17,9 @@ namespace media {
 // data as input and will deinterleave it into the FIFO, and it only allows
 // consuming a whole block of AudioBus element.
 // This class is thread-unsafe.
+//
+// NOTE: Consider using the more-efficient and easier-to-use AudioRechunker
+// instead of this FIFO implementation.
 class MEDIA_EXPORT AudioBlockFifo {
  public:
   // Creates a new AudioBlockFifo and allocates |blocks| memory, each block