Update API for Objective-C RTCMediaStream.

webrtc/api/objc/RTCMediaStream+Private.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 "RTCAudioTrack.h"
+#import "RTCMediaStream.h"
 
 #include "talk/app/webrtc/mediastreaminterface.h"
 
 NS_ASSUME_NONNULL_BEGIN
 
-@interface RTCAudioTrack ()
+@interface RTCMediaStream ()
 
-/** AudioTrackInterface created or passed in at construction. */
+/**
+ * MediaStreamInterface representation of this RTCMediaStream object. This is
+ * needed to pass to the underlying C++ APIs.
+ */
 @property(nonatomic, readonly)
-    rtc::scoped_refptr<webrtc::AudioTrackInterface> nativeAudioTrack;
+    rtc::scoped_refptr<webrtc::MediaStreamInterface> nativeMediaStream;
+
+/** Initialize an RTCMediaStream from a native MediaStreamInterface. */
+- (instancetype)initWithNativeMediaStream:
+    (rtc::scoped_refptr<webrtc::MediaStreamInterface>)nativeMediaStream;
 
 @end
 
 NS_ASSUME_NONNULL_END