Add AVFoundation video capture support to Mac objc SDK (based on iOS)

webrtc/sdk/objc/Framework/Classes/RTCPeerConnectionFactory.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.
  */
 
 #import "RTCPeerConnectionFactory+Private.h"
 
 #import "NSString+StdString.h"
-#if defined(WEBRTC_IOS)
 #import "RTCAVFoundationVideoSource+Private.h"
-#endif
 #import "RTCAudioTrack+Private.h"
 #import "RTCMediaStream+Private.h"
 #import "RTCPeerConnection+Private.h"
 #import "RTCVideoSource+Private.h"
 #import "RTCVideoTrack+Private.h"
 
 #include <memory>
 
 @implementation RTCPeerConnectionFactory {
   std::unique_ptr<rtc::Thread> _networkThread;
@@ skipping 20 matching lines @@
     _nativeFactory = webrtc::CreatePeerConnectionFactory(
         _networkThread.get(), _workerThread.get(), _signalingThread.get(),
         nullptr, nullptr, nullptr);
     NSAssert(_nativeFactory, @"Failed to initialize PeerConnectionFactory!");
   }
   return self;
 }
 
 - (RTCAVFoundationVideoSource *)avFoundationVideoSourceWithConstraints:
     (nullable RTCMediaConstraints *)constraints {
-#if defined(WEBRTC_IOS)
   return [[RTCAVFoundationVideoSource alloc] initWithFactory:self
                                                  constraints:constraints];
-#else
-  return nil;
-#endif
 }
 
 - (RTCAudioTrack *)audioTrackWithTrackId:(NSString *)trackId {
   return [[RTCAudioTrack alloc] initWithFactory:self
                                         trackId:trackId];
 }
 
 - (RTCVideoTrack *)videoTrackWithSource:(RTCVideoSource *)source
                                 trackId:(NSString *)trackId {
   return [[RTCVideoTrack alloc] initWithFactory:self
@@ skipping 12 matching lines @@
     (RTCMediaConstraints *)constraints
                                               delegate:
     (nullable id<RTCPeerConnectionDelegate>)delegate {
   return [[RTCPeerConnection alloc] initWithFactory:self
                                       configuration:configuration
                                         constraints:constraints
                                            delegate:delegate];
 }
 
 @end