MacOS: Add metal renderer and view.

webrtc/sdk/objc/Framework/Headers/WebRTC/RTCMTLNSVideoView.h

Index: webrtc/sdk/objc/Framework/Headers/WebRTC/RTCMTLNSVideoView.h
diff --git a/webrtc/sdk/objc/Framework/Headers/WebRTC/RTCMTLNSVideoView.h b/webrtc/sdk/objc/Framework/Headers/WebRTC/RTCMTLNSVideoView.h
new file mode 100644
index 0000000000000000000000000000000000000000..ba4880ff9472326878c9dfe88cce4f37656c0e02
--- /dev/null
+++ b/webrtc/sdk/objc/Framework/Headers/WebRTC/RTCMTLNSVideoView.h
@@ -0,0 +1,17 @@
+/*
+ *  Copyright 2017 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 <Cocoa/Cocoa.h>
+#import "WebRTC/RTCVideoRenderer.h"
+
+NS_AVAILABLE_MAC(10.11)
+@interface RTCMTLNSVideoView : NSView <RTCVideoRenderer>
+
+@end