Add metal view, shaders and renderer.

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

Index: webrtc/sdk/objc/Framework/Headers/WebRTC/RTCMTLVideoView.h
diff --git a/webrtc/sdk/objc/Framework/Headers/WebRTC/RTCMTLVideoView.h b/webrtc/sdk/objc/Framework/Headers/WebRTC/RTCMTLVideoView.h
new file mode 100644
index 0000000000000000000000000000000000000000..14a7077c8c96ecde9a77a156523e62a3a083e74b
--- /dev/null
+++ b/webrtc/sdk/objc/Framework/Headers/WebRTC/RTCMTLVideoView.h
@@ -0,0 +1,33 @@
+/*
+ *  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 <Foundation/Foundation.h>
+
+#import "WebRTC/RTCVideoRenderer.h"
+
+NS_ASSUME_NONNULL_BEGIN
+RTC_EXPORT
+
+/**
+ * RTCMTLVideoView is thin wrapper around MTKView.
+ *
+ * It has id<RTCVideoRenderer> property that renders video frames in the view's
+ * bounds using Metal.
+ */
+NS_CLASS_AVAILABLE_IOS(9)
+@interface RTCMTLVideoView : UIView
+
+/**
+ * Renderer class that can render RTCVideoTrack.
+ */
+@property(nonatomic, readonly) id<RTCVideoRenderer> renderer;

[tkchin_webrtc, 2017/02/16 23:28:04]

For the purposes of landing this CL, can we remove this property first, or
otherwise make it private?
We have a meeting next week to chat about pending work, and one of the items is
how to pass in shaders, and how to make it so that it's possible to chain
shaders.

In this CL, can we make it so that a metal renderer view is initialized like so
(basically old behavior):

RTCMTLVideoView *videoView = [[RTCMTLVideoView alloc] initWithFrame:frame];
rtcVideoTrack.renderer = videoView;

As opposed to the current setup where we need to also create a renderer and pass
it in, which is really the creation of a shader and passing it in. We can
imagine adding a new ctor to RTCMTLVideoView like initWithFrame:shader: in the
future, and that should work easily with old init method (old init method just
uses NV12 shader by default).

+
+@end
+NS_ASSUME_NONNULL_END