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

webrtc/audio_state.h

Index: webrtc/audio_state.h
diff --git a/webrtc/audio_state.h b/webrtc/audio_state.h
index c6168237a9a1153a6868570b9adcc226d484f46e..fa5784c84492212dcbce55f58ede889597aed185 100644
--- a/webrtc/audio_state.h
+++ b/webrtc/audio_state.h
@@ -18,6 +18,11 @@ namespace webrtc {
 class AudioDeviceModule;
 class VoiceEngine;
 
+// 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.
+// See: https://bugs.chromium.org/p/webrtc/issues/detail?id=4690
+
 // AudioState holds the state which must be shared between multiple instances of
 // webrtc::Call for audio processing purposes.
 class AudioState : public rtc::RefCountInterface {