Tweaks for new Objective-C API.

webrtc/api/objc/RTCMediaStream.mm

Index: webrtc/api/objc/RTCMediaStream.mm
diff --git a/webrtc/api/objc/RTCMediaStream.mm b/webrtc/api/objc/RTCMediaStream.mm
index dcdef9d1a456438f6b1ab8ed503593361e6224f1..3c3e4d906455cedbc4e343d086df6903007f12a2 100644
--- a/webrtc/api/objc/RTCMediaStream.mm
+++ b/webrtc/api/objc/RTCMediaStream.mm
@@ -15,6 +15,7 @@
 #import "webrtc/api/objc/RTCAudioTrack+Private.h"
 #import "webrtc/api/objc/RTCMediaStream+Private.h"
 #import "webrtc/api/objc/RTCMediaStreamTrack+Private.h"
+#import "webrtc/api/objc/RTCPeerConnectionFactory+Private.h"
 #import "webrtc/api/objc/RTCVideoTrack+Private.h"
 #import "webrtc/base/objc/NSString+StdString.h"
 
@@ -26,6 +27,16 @@
   rtc::scoped_refptr<webrtc::MediaStreamInterface> _nativeMediaStream;
 }
 
+- (instancetype)initWithFactory:(RTCPeerConnectionFactory *)factory
+                       streamId:(NSString *)streamId {
+  NSParameterAssert(factory);
+  NSParameterAssert(streamId.length);
+  std::string nativeId = [NSString stdStringForString:streamId];
+  rtc::scoped_refptr<webrtc::MediaStreamInterface> stream =
+      factory.nativeFactory->CreateLocalMediaStream(nativeId);
+  return [self initWithNativeMediaStream:stream];
+}
+
 - (NSArray *)audioTracks {
 // - (NSArray<RTCAudioTrack *> *)audioTracks {
   return [_audioTracks copy];