Update API for Objective-C RTCDataChannelConfiguration.

BUG=

Review URL: https://codereview.webrtc.org/1616363005

Cr-Commit-Position: refs/heads/master@{#11405}
diff --git a/webrtc/api/objc/RTCDataChannelConfiguration+Private.h b/webrtc/api/objc/RTCDataChannelConfiguration+Private.h
new file mode 100644
index 0000000..e99ba7c
--- /dev/null
+++ b/webrtc/api/objc/RTCDataChannelConfiguration+Private.h
@@ -0,0 +1,23 @@
+/*
+ *  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 "RTCDataChannelConfiguration.h"
+
+#include "talk/app/webrtc/datachannelinterface.h"
+
+NS_ASSUME_NONNULL_BEGIN
+
+@interface RTCDataChannelConfiguration ()
+
+@property(nonatomic, readonly) webrtc::DataChannelInit nativeDataChannelInit;
+
+@end
+
+NS_ASSUME_NONNULL_END