Add HeaderExtensions to RtpParameters

Bug: webrtc:7580
Change-Id: I4fcf3e8bc4975a6b2baa6f24a17c254d2bf521d9
Reviewed-on: https://webrtc-review.googlesource.com/78288
Commit-Queue: Florent Castelli <orphis@webrtc.org>
Reviewed-by: Sami Kalliomäki <sakal@webrtc.org>
Reviewed-by: Anders Carlsson <andersc@webrtc.org>
Reviewed-by: Taylor Brandstetter <deadbeef@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23584}

sdk/objc/Framework/Classes/PeerConnection/RTCRtpHeaderExtension+Private.h

@@ -0,0 +1,27 @@
+/*
+ *  Copyright 2018 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 "WebRTC/RTCRtpHeaderExtension.h"
+
+#include "api/rtpparameters.h"
+
+NS_ASSUME_NONNULL_BEGIN
+
+@interface RTCRtpHeaderExtension ()
+
+/** Returns the equivalent native RtpExtension structure. */
+@property(nonatomic, readonly) webrtc::RtpExtension nativeParameters;
+
+/** Initialize the object with a native RtpExtension structure. */
+- (instancetype)initWithNativeParameters:(const webrtc::RtpExtension &)nativeParameters;
+
+@end
+
+NS_ASSUME_NONNULL_END