Compile rtc_api_objc on Mac.

webrtc/api/objc/RTCMediaStream.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.
  */
 
 #import <Foundation/Foundation.h>
 
 NS_ASSUME_NONNULL_BEGIN
+// TODO(hjon): Update nullability types. See http://crbug/webrtc/5592
 
 @class RTCAudioTrack;
 @class RTCVideoTrack;
 
 @interface RTCMediaStream : NSObject
 
 /** The audio tracks in this stream. */
-@property(nonatomic, strong, readonly) NSArray<RTCAudioTrack *> *audioTracks;
+@property(nonatomic, strong, readonly) NSArray *audioTracks;
+// @property(nonatomic, strong, readonly) NSArray<RTCAudioTrack *> *audioTracks;
 
 /** The video tracks in this stream. */
-@property(nonatomic, strong, readonly) NSArray<RTCVideoTrack *> *videoTracks;
+@property(nonatomic, strong, readonly) NSArray *videoTracks;
+// @property(nonatomic, strong, readonly) NSArray<RTCVideoTrack *> *videoTracks;
 
 /** An identifier for this media stream. */
 @property(nonatomic, readonly) NSString *streamId;
 
 - (instancetype)init NS_UNAVAILABLE;
 
 /** Adds the given audio track to this media stream. */
 - (void)addAudioTrack:(RTCAudioTrack *)audioTrack;
 
 /** Adds the given video track to this media stream. */
 - (void)addVideoTrack:(RTCVideoTrack *)videoTrack;
 
 /** Removes the given audio track to this media stream. */
 - (void)removeAudioTrack:(RTCAudioTrack *)audioTrack;
 
 /** Removes the given video track to this media stream. */
 - (void)removeVideoTrack:(RTCVideoTrack *)videoTrack;
 
 @end
 
 NS_ASSUME_NONNULL_END