Add isolate tag-profile and better handling of errors

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 72 matching lines @@
     sendRootServiceMessage(request);
     return _completer.future;
   }
 
   void setResponse(String response) {
     _completer.complete(response);
   }
 
   void setErrorResponse(String error) {
     _completer.complete(JSON.encode({
-        'type': 'Error',
-        'msg': error,
+        'type': 'ServiceError',
+        'id': '',
+        'kind': 'RequestError',
+        'message': error,
         'path': path,
         'options': options
     }));
   }
 }
 
 void sendIsolateServiceMessage(SendPort sp, List m)
     native "VMService_SendIsolateServiceMessage";
 
 void sendRootServiceMessage(List m)
     native "VMService_SendRootServiceMessage";