Include a "jsonrpc" property in all VM service responses.

runtime/vm/service/message.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of vmservice;
 
 class Message {
   final Completer _completer = new Completer.sync();
   bool get completed => _completer.isCompleted;
   /// Future of response.
@@ skipping 125 matching lines @@
     sendRootServiceMessage(request);
     return _completer.future;
   }
 
   void setResponse(String response) {
     _completer.complete(response);
   }
 
   void setErrorResponse(String message) {
     var response = {
+      'jsonrpc': '2.0',
       'id': serial,
       'result' : {
         'type': 'Error',
         'message': message,
         'request': {
           'method': method,
           'params': params
         }
       }
     };
     _completer.complete(JSON.encode(response));
   }
 }
 
 bool sendIsolateServiceMessage(SendPort sp, List m)
     native "VMService_SendIsolateServiceMessage";
 
 void sendRootServiceMessage(List m)
     native "VMService_SendRootServiceMessage";