Added the API to create an RTCRtpSender to the Objective C wrapper.

webrtc/sdk/objc/Framework/Classes/RTCMediaStreamTrack.mm

 /*
  *  Copyright 2015 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 #import "RTCMediaStreamTrack+Private.h"
 
 #import "NSString+StdString.h"
 
+NSString * const kRTCMediaStreamTrackKindAudio =
+    @(webrtc::MediaStreamTrackInterface::kAudioKind);
+NSString * const kRTCMediaStreamTrackKindVideo =
+    @(webrtc::MediaStreamTrackInterface::kVideoKind);
+
 @implementation RTCMediaStreamTrack {
   rtc::scoped_refptr<webrtc::MediaStreamTrackInterface> _nativeTrack;
   RTCMediaStreamTrackType _type;
 }
 
 - (NSString *)kind {
   return [NSString stringForStdString:_nativeTrack->kind()];
 }
 
 - (NSString *)trackId {
@@ skipping 98 matching lines @@
 + (NSString *)stringForState:(RTCMediaStreamTrackState)state {
   switch (state) {
     case RTCMediaStreamTrackStateLive:
       return @"Live";
     case RTCMediaStreamTrackStateEnded:
       return @"Ended";
   }
 }
 
 @end