Implement PeerConnection::AddTrack/RemoveTrack for Unified Plan

Bug: webrtc:7600
Change-Id: I2a48426a29ac67b6bdbd7817fe07273cdd5fd980
Reviewed-on: https://webrtc-review.googlesource.com/31647
Commit-Queue: Steve Anton <steveanton@webrtc.org>
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Peter Thatcher <pthatcher@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21305}
diff --git a/api/peerconnectionproxy.h b/api/peerconnectionproxy.h
index 1d8cf5f..c39c933 100644
--- a/api/peerconnectionproxy.h
+++ b/api/peerconnectionproxy.h
@@ -28,6 +28,10 @@
   PROXY_METHOD0(rtc::scoped_refptr<StreamCollectionInterface>, remote_streams)
   PROXY_METHOD1(bool, AddStream, MediaStreamInterface*)
   PROXY_METHOD1(void, RemoveStream, MediaStreamInterface*)
+  PROXY_METHOD2(RTCErrorOr<rtc::scoped_refptr<RtpSenderInterface>>,
+                AddTrackWithStreamLabels,
+                rtc::scoped_refptr<MediaStreamTrackInterface>,
+                const std::vector<std::string>&);
   PROXY_METHOD2(rtc::scoped_refptr<RtpSenderInterface>,
                 AddTrack,
                 MediaStreamTrackInterface*,