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

webrtc/api/objc/RTCVideoRenderer.h

Index: webrtc/api/objc/RTCVideoRenderer.h
diff --git a/webrtc/base/objc/NSString+StdString.h b/webrtc/api/objc/RTCVideoRenderer.h
similarity index 66%
copy from webrtc/base/objc/NSString+StdString.h
copy to webrtc/api/objc/RTCVideoRenderer.h
index 8bf6cc94be0346e398ab1a980af6378f06ccb7a5..a97456275a8c7e6ca10cd50714b35b92462c9d4b 100644
--- a/webrtc/base/objc/NSString+StdString.h
+++ b/webrtc/api/objc/RTCVideoRenderer.h
@@ -9,17 +9,21 @@
  */
 
 #import <Foundation/Foundation.h>
-
-#include <string>
+#if TARGET_OS_IPHONE
+#import <UIKit/UIKit.h>
+#endif
 
 NS_ASSUME_NONNULL_BEGIN
 
-@interface NSString (StdString)
+@class RTCVideoFrame;
+
+@protocol RTCVideoRenderer <NSObject>
 
-@property(nonatomic, readonly) std::string stdString;
+/** The size of the frame. */
+- (void)setSize:(CGSize)size;
 
-+ (std::string)stdStringForString:(NSString *)nsString;
-+ (NSString *)stringForStdString:(const std::string&)stdString;
+/** The frame to be displayed. */
+- (void)renderFrame:(RTCVideoFrame *)frame;
 
 @end