Add metal view, shaders and renderer.

webrtc/sdk/objc/Framework/Classes/metal/RTCMTLVideoView.m

+/*
+ *  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 "WebRTC/RTCMTLVideoView.h"
+
+#import <Metal/Metal.h>
+
+#import "RTCNV12Renderer.h"
+
+@interface RTCMTLVideoView ()
+@property(nonatomic) id<RTCMTLRenderer> renderer;
+@end
+
+@implementation RTCMTLVideoView {
+  id<RTCMTLRenderer> _renderer;
+}
+
+@synthesize renderer = _renderer;
+
+- (instancetype)initWithFrame:(CGRect)frameRect device:(nullable id<MTLDevice>)device {
+  self = [super initWithFrame:frameRect device:device];
+  if (self) {
+    _renderer = [[RTCNV12Renderer alloc] initWithView:self];
+  }
+  return self;
+}
+
+- (BOOL)setupRenderer {
+  return [_renderer setup];
+}
+
+@end