Tweaks for new Objective-C API.

webrtc/api/objc/RTCMediaStream.h

Index: webrtc/api/objc/RTCMediaStream.h
diff --git a/webrtc/api/objc/RTCMediaStream.h b/webrtc/api/objc/RTCMediaStream.h
index b3143604340af9a3141642369bb9c828489fdd92..7df1ea8ea80ee8c12d419a210f4548d2e5deccc0 100644
--- a/webrtc/api/objc/RTCMediaStream.h
+++ b/webrtc/api/objc/RTCMediaStream.h
@@ -14,6 +14,7 @@ NS_ASSUME_NONNULL_BEGIN
 // TODO(hjon): Update nullability types. See http://crbug/webrtc/5592
 
 @class RTCAudioTrack;
+@class RTCPeerConnectionFactory;
 @class RTCVideoTrack;
 
 @interface RTCMediaStream : NSObject
@@ -31,6 +32,10 @@ NS_ASSUME_NONNULL_BEGIN
 
 - (instancetype)init NS_UNAVAILABLE;
 
+/** Initialize an RTCMediaStream with an id. */
+- (instancetype)initWithFactory:(RTCPeerConnectionFactory *)factory
+                       streamId:(NSString *)streamId;
+
 /** Adds the given audio track to this media stream. */
 - (void)addAudioTrack:(RTCAudioTrack *)audioTrack;