Mark public ObjC APIs as explicitly visible.

webrtc/api/objc/RTCVideoFrame.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 <AVFoundation/AVFoundation.h>
 #import <Foundation/Foundation.h>
 
+#import "webrtc/base/objc/RTCMacros.h"
+
 NS_ASSUME_NONNULL_BEGIN
 
 // RTCVideoFrame is an ObjectiveC version of cricket::VideoFrame.
+RTC_EXPORT
 @interface RTCVideoFrame : NSObject
 
 /** Width without rotation applied. */
 @property(nonatomic, readonly) size_t width;
 
 /** Height without rotation applied. */
 @property(nonatomic, readonly) size_t height;
 @property(nonatomic, readonly) size_t chromaWidth;
 @property(nonatomic, readonly) size_t chromaHeight;
 // These can return NULL if the object is not backed by a buffer.
@@ skipping 13 matching lines @@
 - (instancetype)init NS_UNAVAILABLE;
 
 /** If the frame is backed by a CVPixelBuffer, creates a backing i420 frame.
  *  Calling the yuv plane properties will call this method if needed.
  */
 - (void)convertBufferIfNeeded;
 
 @end
 
 NS_ASSUME_NONNULL_END