Base A/V synchronization on sync_labels.

webrtc/audio_receive_stream.h

Index: webrtc/audio_receive_stream.h
diff --git a/webrtc/audio_receive_stream.h b/webrtc/audio_receive_stream.h
index c68d2647f20beb2142877558686764783f4b6571..c628c1d480a9c2976d76b924a0b6fef9bbe1a3da 100644
--- a/webrtc/audio_receive_stream.h
+++ b/webrtc/audio_receive_stream.h
@@ -43,6 +43,15 @@ class AudioReceiveStream {
       std::vector<RtpExtension> extensions;
     } rtp;
 
+    // Handle to underlying VoiceEngine handle, used to map AudioReceiveStream
+    // to lower-level components.
+    int channel_id = -1;
+
+    // Identifier for an A/V synchronization group. Empty string to disable.
+    // TODO(pbos): Synchronize streams in a sync group, not just video streams
+    // to one of the audio streams.
+    std::string sync_group;
+
     // Decoders for every payload that we can receive. Call owns the
     // AudioDecoder instances once the Config is submitted to
     // Call::CreateReceiveStream().