Update API for Objective-C RTCConfiguration.

BUG=

Review URL: https://codereview.webrtc.org/1616303002

Cr-Commit-Position: refs/heads/master@{#11386}
diff --git a/webrtc/api/objc/RTCIceServer+Private.h b/webrtc/api/objc/RTCIceServer+Private.h
index 59f5a92..3890567 100644
--- a/webrtc/api/objc/RTCIceServer+Private.h
+++ b/webrtc/api/objc/RTCIceServer+Private.h
@@ -23,6 +23,10 @@
 @property(nonatomic, readonly)
     webrtc::PeerConnectionInterface::IceServer iceServer;
 
+/** Initialize an RTCIceServer from a native IceServer. */
+- (instancetype)initWithNativeServer:
+    (webrtc::PeerConnectionInterface::IceServer)nativeServer;
+
 @end
 
 NS_ASSUME_NONNULL_END