Add comments about the Audio parts of the public Call API being WIP.

webrtc/audio_send_stream.h

Index: webrtc/audio_send_stream.h
diff --git a/webrtc/audio_send_stream.h b/webrtc/audio_send_stream.h
index c5db82b91bbf156733967831181a8b5f41ecd28b..ced77016faa2a3fbba24527e0e9da1c0132aa8cf 100644
--- a/webrtc/audio_send_stream.h
+++ b/webrtc/audio_send_stream.h
@@ -23,6 +23,10 @@
 
 namespace webrtc {
 
+// WORK IN PROGRESS
+// This class is under development and is not yet intended for for use outside
+// of WebRtc/Libjingle. Please use the VoiceEngine API instead.
+
 class AudioSendStream : public SendStream {
  public:
   struct Stats {