Move Objective-C video renderers to webrtc/api/objc.

webrtc/api/objc/RTCNSGLVideoView.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 <Foundation/Foundation.h>
+#if TARGET_OS_IPHONE
+#error "This file targets OSX."
+#endif
 
-#include <string>
+#import <AppKit/NSOpenGLView.h>
+
+#import "RTCVideoRenderer.h"
 
 NS_ASSUME_NONNULL_BEGIN
 
-@interface NSString (StdString)
+@class RTCNSGLVideoView;
+@protocol RTCNSGLVideoViewDelegate
 
-@property(nonatomic, readonly) std::string stdString;
-
-+ (std::string)stdStringForString:(NSString *)nsString;
-+ (NSString *)stringForStdString:(const std::string&)stdString;
+- (void)videoView:(RTCNSGLVideoView *)videoView didChangeVideoSize:(CGSize)size;
 
 @end
 
+@interface RTCNSGLVideoView : NSOpenGLView <RTCVideoRenderer>
+
+@property(nonatomic, weak) id<RTCNSGLVideoViewDelegate> delegate;
+
+@end
+
 NS_ASSUME_NONNULL_END