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

webrtc/sdk/objc/Framework/Headers/WebRTC/RTCPeerConnection.h

 /*
  *  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.
  */
 
@@ skipping 153 matching lines @@
           completionHandler:
     (nullable void (^)(NSError * _Nullable error))completionHandler;
 
 /** Apply the supplied RTCSessionDescription as the remote description. */
 - (void)setRemoteDescription:(RTCSessionDescription *)sdp
            completionHandler:
     (nullable void (^)(NSError * _Nullable error))completionHandler;
 
 @end
 
+@interface RTCPeerConnection (Media)
+
+/** Create an RTCRtpSender with the specified kind and media stream ID. */
+- (RTCRtpSender *)senderWithKind:(NSString *)kind streamId:(NSString *)streamId;
+
+@end
+
 @interface RTCPeerConnection (DataChannel)
 
 /** Create a new data channel with the given label and configuration. */
 - (RTCDataChannel *)dataChannelForLabel:(NSString *)label
     configuration:(RTCDataChannelConfiguration *)configuration;
 
 @end
 
 @interface RTCPeerConnection (Stats)
 
 /** Gather stats for the given RTCMediaStreamTrack. If |mediaStreamTrack| is nil
  *  statistics are gathered for all tracks.
  */
 - (void)statsForTrack:
     (nullable RTCMediaStreamTrack *)mediaStreamTrack
      statsOutputLevel:(RTCStatsOutputLevel)statsOutputLevel
     completionHandler:
     (nullable void (^)(NSArray<RTCStatsReport *> *stats))completionHandler;
 
 @end
 
 NS_ASSUME_NONNULL_END