Fix the broken XML parser due to version mismatch.

components/update_client/update_response.h

 // Copyright 2014 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.
 
 #ifndef COMPONENTS_UPDATE_CLIENT_UPDATE_RESPONSE_H_
 #define COMPONENTS_UPDATE_CLIENT_UPDATE_RESPONSE_H_
 
 #include <map>
 #include <memory>
 #include <string>
 #include <vector>
 
 #include "base/macros.h"
 #include "url/gurl.h"
 
 namespace update_client {
 
+// The protocol versions so far are:
+// * Version 3.1: it changes how the run actions are serialized.
+// * Version 3.0: it is the version implemented by the desktop updaters.
+constexpr char kProtocolVersion[] = "3.1";
+
 // Parses responses for the update protocol version 3.
 // (https://github.com/google/omaha/blob/wiki/ServerProtocolV3.md)
 //
 // An update response looks like this:
 //
 // <?xml version="1.0" encoding="UTF-8"?>
 //  <response protocol="3.0" server="prod">
 //    <daystart elapsed_seconds="56508"/>
 //    <app appid="{430FD4D0-B729-4F61-AA34-91526481799D}" status="ok">
 //      <updatecheck status="noupdate"/>
@@ skipping 124 matching lines @@
 
   // Adds parse error details to |errors_| string.
   void ParseError(const char* details, ...);
 
   DISALLOW_COPY_AND_ASSIGN(UpdateResponse);
 };
 
 }  // namespace update_client
 
 #endif  // COMPONENTS_UPDATE_CLIENT_UPDATE_RESPONSE_H_