Add signaling to support ICE renomination.

webrtc/api/peerconnection.h

Index: webrtc/api/peerconnection.h
diff --git a/webrtc/api/peerconnection.h b/webrtc/api/peerconnection.h
index c4a9a60053db82ca9976340412334e70bae55a59..042e7f1bd43f539aa14cd7f4cc8b1c096ee9b1d7 100644
--- a/webrtc/api/peerconnection.h
+++ b/webrtc/api/peerconnection.h
@@ -239,6 +239,9 @@ class PeerConnection : public PeerConnectionInterface,
       const RTCOfferAnswerOptions& options,
       cricket::MediaSessionOptions* session_options);
 
+  void InitializeOptionsForAnswer(
+      cricket::MediaSessionOptions* session_options);
+
   // Helper function for options processing.
   // Deprecated.
   virtual void FinishOptionsForAnswer(
@@ -414,6 +417,8 @@ class PeerConnection : public PeerConnectionInterface,
 
   bool remote_peer_supports_msid_ = false;
 
+  bool enable_ice_renomination_ = false;
+
   std::vector<rtc::scoped_refptr<RtpSenderProxyWithInternal<RtpSenderInternal>>>
       senders_;
   std::vector<