Clear the channel and endpoint_id in SetAddress for the XMPP channel.

remoting/protocol/jingle_messages.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "remoting/protocol/jingle_messages.h"
 
 #include "base/logging.h"
 #include "base/strings/string_number_conversions.h"
 #include "remoting/base/constants.h"
 #include "remoting/protocol/content_description.h"
@@ skipping 184 matching lines @@
     return empty_instance;
   }
 
   return SignalingAddress(jid, endpoint_id, channel);
 }
 
 void SetAddress(buzz::XmlElement* iqElement,
                 const SignalingAddress& address,
                 bool from) {
   if (address.empty()) {
+    iqElement->ClearAttr(GetQNameByField(Field::JID, from));
+    iqElement->ClearAttr(GetQNameByField(Field::CHANNEL, from));
+    iqElement->ClearAttr(GetQNameByField(Field::ENDPOINT_ID, from));

[Jamie, 2016/05/20 00:48:35]

I think it might be clearer to clear everything up-front with a comment
explaining that you want to start from a fresh state, regardless of the previous
address format. Then add in the components that make sense for the new format.

     return;
   }
 
   iqElement->AddAttr(GetQNameByField(Field::JID, from), address.jid);
 
   if (address.channel == SignalingAddress::Channel::LCS) {
     iqElement->AddAttr(GetQNameByField(Field::ENDPOINT_ID, from),
                        address.endpoint_id);
     const char* channel_str = ValueToName(kChannelTypes, address.channel);
     iqElement->AddAttr(GetQNameByField(Field::CHANNEL, from), channel_str);
+  } else {
+    iqElement->ClearAttr(GetQNameByField(Field::CHANNEL, from));
+    iqElement->ClearAttr(GetQNameByField(Field::ENDPOINT_ID, from));
   }
 }
 
 }  // namespace
 
 IceTransportInfo::NamedCandidate::NamedCandidate(
     const std::string& name,
     const cricket::Candidate& candidate)
     : name(name),
       candidate(candidate) {
@@ skipping 368 matching lines @@
     result->AddElement(FormatIceCredentials(credentials));
   }
   for (const NamedCandidate& candidate : candidates) {
     result->AddElement(FormatIceCandidate(candidate));
   }
   return result;
 }
 
 }  // namespace protocol
 }  // namespace remoting