Adding AddTrack/RemoveTrack to native PeerConnection API.

Also, now creating the RtpSender/RtpReceiver proxy objects immediately,
rather than waiting until when GetSenders/GetReceivers is called.

Review URL: https://codereview.webrtc.org/1563403002

Cr-Commit-Position: refs/heads/master@{#11259}
diff --git a/talk/app/webrtc/peerconnectionproxy.h b/talk/app/webrtc/peerconnectionproxy.h
index 3c983d7..d76a6b8 100644
--- a/talk/app/webrtc/peerconnectionproxy.h
+++ b/talk/app/webrtc/peerconnectionproxy.h
@@ -41,6 +41,11 @@
                 remote_streams)
   PROXY_METHOD1(bool, AddStream, MediaStreamInterface*)
   PROXY_METHOD1(void, RemoveStream, MediaStreamInterface*)
+  PROXY_METHOD2(rtc::scoped_refptr<RtpSenderInterface>,
+                AddTrack,
+                MediaStreamTrackInterface*,
+                std::vector<MediaStreamInterface*>)
+  PROXY_METHOD1(bool, RemoveTrack, RtpSenderInterface*)
   PROXY_METHOD1(rtc::scoped_refptr<DtmfSenderInterface>,
                 CreateDtmfSender, AudioTrackInterface*)
   PROXY_METHOD2(rtc::scoped_refptr<RtpSenderInterface>,