iOS: add type to peer connection local streams

webrtc/sdk/objc/Framework/Classes/RTCPeerConnection.mm

 /*
  *  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 186 matching lines @@
   }
   RTCPeerConnection* peer_connection = peer_connection_;
   [peer_connection.delegate peerConnection:peer_connection
                     didRemoveIceCandidates:ice_candidates];
 }
 
 }  // namespace webrtc
 
 
 @implementation RTCPeerConnection {
-  NSMutableArray *_localStreams;
+  NSMutableArray<RTCMediaStream *> *_localStreams;
   std::unique_ptr<webrtc::PeerConnectionDelegateAdapter> _observer;
   rtc::scoped_refptr<webrtc::PeerConnectionInterface> _peerConnection;
   BOOL _hasStartedRtcEventLog;
 }
 
 @synthesize delegate = _delegate;
 
 - (instancetype)initWithFactory:(RTCPeerConnectionFactory *)factory
                   configuration:(RTCConfiguration *)configuration
                     constraints:(RTCMediaConstraints *)constraints
@@ skipping 16 matching lines @@
                                                     _observer.get());
     if (!_peerConnection) {
       return nil;
     }
     _localStreams = [[NSMutableArray alloc] init];
     _delegate = delegate;
   }
   return self;
 }
 
-- (NSArray *)localStreams {
+- (NSArray<RTCMediaStream *> *)localStreams {
   return [_localStreams copy];
 }
 
 - (RTCSessionDescription *)localDescription {
   const webrtc::SessionDescriptionInterface *description =
       _peerConnection->local_description();
   return description ?
       [[RTCSessionDescription alloc] initWithNativeDescription:description]
           : nil;
 }
@@ skipping 328 matching lines @@
     case RTCStatsOutputLevelDebug:
       return webrtc::PeerConnectionInterface::kStatsOutputLevelDebug;
   }
 }
 
 - (rtc::scoped_refptr<webrtc::PeerConnectionInterface>)nativePeerConnection {
   return _peerConnection;
 }
 
 @end