MacOS: Add metal renderer and view.

webrtc/examples/objc/AppRTCMobile/mac/APPRTCViewController.m

Index: webrtc/examples/objc/AppRTCMobile/mac/APPRTCViewController.m
diff --git a/webrtc/examples/objc/AppRTCMobile/mac/APPRTCViewController.m b/webrtc/examples/objc/AppRTCMobile/mac/APPRTCViewController.m
index bcf26b258e745076693a60778653b98b5cc83dbf..28ac9e29321ab81a7fd151fa5bdc801747b138ec 100644
--- a/webrtc/examples/objc/AppRTCMobile/mac/APPRTCViewController.m
+++ b/webrtc/examples/objc/AppRTCMobile/mac/APPRTCViewController.m
@@ -12,6 +12,7 @@
 
 #import <AVFoundation/AVFoundation.h>
 
+#import "WebRTC/RTCMTLNSVideoView.h"
 #import "WebRTC/RTCNSGLVideoView.h"
 #import "WebRTC/RTCVideoTrack.h"
 
@@ -35,7 +36,7 @@ static NSUInteger const kBottomViewHeight = 200;
 
 @property(nonatomic, weak) id<APPRTCMainViewDelegate> delegate;
 @property(nonatomic, readonly) RTCNSGLVideoView* localVideoView;
-@property(nonatomic, readonly) RTCNSGLVideoView* remoteVideoView;
+@property(nonatomic, readonly) NSView<RTCVideoRenderer>* remoteVideoView;
 
 - (void)displayLogMessage:(NSString*)message;
 
@@ -177,7 +178,7 @@ static NSUInteger const kBottomViewHeight = 200;
 #pragma mark - RTCNSGLVideoViewDelegate
 
 - (void)videoView:(RTCNSGLVideoView*)videoView
-    didChangeVideoSize:(NSSize)size {
+didChangeVideoSize:(NSSize)size {

[magjed_webrtc, 2017/03/28 11:20:29]

Indentation must be wrong here?

[daniela-webrtc, 2017/03/28 14:58:05]

Done.

   if (videoView == _remoteVideoView) {
     _remoteVideoSize = size;
   } else if (videoView == _localVideoView) {
@@ -222,10 +223,24 @@ static NSUInteger const kBottomViewHeight = 200;
   };
   NSOpenGLPixelFormat* pixelFormat =
       [[NSOpenGLPixelFormat alloc] initWithAttributes:attributes];
-  _remoteVideoView = [[RTCNSGLVideoView alloc] initWithFrame:NSZeroRect
-                                                 pixelFormat:pixelFormat];
+
+// NOTE (daniela): Ignoring Clang diagonstic here.
+// We're performing run time check to make sure class is available on runtime.
+// If not we're providing sensible default.
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wpartial-availability"
+  if ([RTCMTLNSVideoView class]) {
+    _remoteVideoView = [[RTCMTLNSVideoView alloc] initWithFrame:NSZeroRect];
+  } else {
+    RTCNSGLVideoView* remote =
+        [[RTCNSGLVideoView alloc] initWithFrame:NSZeroRect pixelFormat:pixelFormat];
+    remote.delegate = self;
+    _remoteVideoView = remote;
+  }
+#pragma clang diagnostic pop
+
   [_remoteVideoView setTranslatesAutoresizingMaskIntoConstraints:NO];
-  _remoteVideoView.delegate = self;
+
   [self addSubview:_remoteVideoView];
 
   _localVideoView = [[RTCNSGLVideoView alloc] initWithFrame:NSZeroRect