Mark public ObjC APIs as explicitly visible.

webrtc/api/objc/RTCDataChannelConfiguration.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 <AvailabilityMacros.h>
 #import <Foundation/Foundation.h>
 
+#import "webrtc/base/objc/RTCMacros.h"
+
 NS_ASSUME_NONNULL_BEGIN
 
+RTC_EXPORT
 @interface RTCDataChannelConfiguration : NSObject
 
 /** Set to YES if ordered delivery is required. */
 @property(nonatomic, assign) BOOL isOrdered;
 
 /** Deprecated. Use maxPacketLifeTime. */
 @property(nonatomic, assign) NSInteger maxRetransmitTimeMs DEPRECATED_ATTRIBUTE;
 
 /**
  * Max period in milliseconds in which retransmissions will be sent. After this
@@ skipping 14 matching lines @@
 
 /** The id of the data channel. */
 @property(nonatomic, assign) int channelId;
 
 /** Set by the application and opaque to the WebRTC implementation. */
 @property(nonatomic) NSString *protocol;
 
 @end
 
 NS_ASSUME_NONNULL_END