Do not JSON encode the 'result' of a service rpc.

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 15 matching lines @@
       return;
     }
     pathSegments.forEach((String segment) {
       if (segment == null || segment == '') {
         return;
       }
       path.add(segment);
     });
   }
 
-  Message.fromJsonRpc(Map map) : serial = map['id'], method = map['method'] {
+  Message.fromJsonRpc(Map map)
+      : serial = map['id'], method = map['method'] {
     params.addAll(map['params']);
   }
 
   static String _methodNameFromUri(Uri uri) {
     if (uri == null) {
       return '';
     }
     if (uri.pathSegments.length == 0) {
       return '';
     }
     return uri.pathSegments[0];
   }
 
-  Message.fromUri(Uri uri) : method = _methodNameFromUri(uri) {
+  Message.fromUri(Uri uri)
+      : method = _methodNameFromUri(uri) {
     params.addAll(uri.queryParameters);
   }
 
   dynamic toJson() {
     return {
       'path': path,
       'params': params
     };
   }
 
@@ skipping 16 matching lines @@
 
   Future<String> send(SendPort sendPort) {
     final receivePort = new RawReceivePort();
     receivePort.handler = (value) {
       receivePort.close();
       assert(value is String);
       _completer.complete(value);
     };
     var keys = _makeAllString(params.keys.toList(growable:false));
     var values = _makeAllString(params.values.toList(growable:false));
-    var request = new List(5)
+    var request = new List(6)
         ..[0] = 0  // Make room for OOB message type.
         ..[1] = receivePort.sendPort
-        ..[2] = method
-        ..[3] = keys
-        ..[4] = values;
+        ..[2] = serial.toString()
+        ..[3] = method
+        ..[4] = keys
+        ..[5] = values;
     if (!sendIsolateServiceMessage(sendPort, request)) {
       _completer.complete(JSON.encode({
           'type': 'ServiceError',
           'id': '',
           'kind': 'InternalError',
           'message': 'could not send message [${serial}] to isolate',
       }));
     }
     return _completer.future;
   }
 
   Future<String> sendToVM() {
     final receivePort = new RawReceivePort();
     receivePort.handler = (value) {
       receivePort.close();
       assert(value is String);
       _completer.complete(value);
     };
     var keys = _makeAllString(params.keys.toList(growable:false));
     var values = _makeAllString(params.values.toList(growable:false));
-    var request = new List(5)
+    var request = new List(6)
         ..[0] = 0  // Make room for OOB message type.
         ..[1] = receivePort.sendPort
-        ..[2] = method
-        ..[3] = keys
-        ..[4] = values;
+        ..[2] = serial.toString()
+        ..[3] = method
+        ..[4] = keys
+        ..[5] = values;
     sendRootServiceMessage(request);
     return _completer.future;
   }
 
   void setResponse(String response) {
     _completer.complete(response);
   }
 
-  void setErrorResponse(String error) {
-    _completer.complete(JSON.encode({
-        'type': 'ServiceError',
-        'id': '',
-        'kind': 'RequestError',
-        'message': error,
-        'path': path,
-        'params': params
-    }));
+  void setErrorResponse(String message) {
+    var response = {
+      '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";