Update/move RTCVideoRendererAdapter to webrtc/api/objc.

webrtc/api/objc/RTCVideoRendererAdapter.h

+/*
+ *  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 "RTCVideoRenderer.h"
+
+#include "talk/app/webrtc/mediastreaminterface.h"
+
+NS_ASSUME_NONNULL_BEGIN
+
+@interface RTCVideoRendererAdapter : NSObject

[tkchin_webrtc, 2016/01/05 21:59:02]

Consider putting this in RTCVideoRenderer+Private.h
(We've been putting anything that deals with C++ in private headers)

[tkchin_webrtc, 2016/01/05 21:59:02]

doco what this class is used for + update property comments.

e.g.
Creates a webrtc::VideoRendererInterface surface for an RTCVideoRenderer. The
webrtc::VideoRendererInterface is used by WebRTC rendering code - this adapter
adapts calls made to that interface to the RTCVideoRenderer supplied during
construction.

[hjon, 2016/01/08 01:00:52]

Done.

+
+/** The Objective-C video renderer represented by this adapter. */
+@property(nonatomic, readonly) id<RTCVideoRenderer> videoRenderer;
+
+/** The native VideoRendererInterface representing this adapter. */

[tkchin_webrtc, 2016/01/05 21:59:02]

doco: pointer is unsafe and owned by this class

[hjon, 2016/01/08 01:00:52]

Done.

+@property(nonatomic, readonly)
+    webrtc::VideoRendererInterface *nativeVideoRenderer;
+
+- (instancetype)init NS_UNAVAILABLE;
+
+/** Initialize an RTCVideoRendererAdapter with an RTCVideoRenderer. */
+- (instancetype)initWithVideoRenderer:(id<RTCVideoRenderer>)videoRenderer
+    NS_DESIGNATED_INITIALIZER;
+
+@end
+
+NS_ASSUME_NONNULL_END