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 532032b3fca66977290d612f1e998c205cceef00..c07266313a72a3072a5545beae2cb1919eab7cda 100644
--- a/webrtc/base/objc/NSString+StdString.h
+++ b/webrtc/api/objc/RTCVideoRenderer.h
@@ -9,16 +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 RTCI420Frame;
+
+@protocol RTCVideoRenderer <NSObject>
 
-@property(nonatomic, readonly) std::string stdString;
+/** The size of the frame. */
+- (void)setSize:(CGSize)size;
 
-+ (std::string)stdStringForString:(NSString *)nsString;
+/** The frame to be displayed. */
+- (void)renderFrame:(RTCI420Frame *)frame;
 
 @end