Make VM service id handling JSON-RPC 2 compliant.

runtime/bin/vmservice/server.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_io;
 
 class WebSocketClient extends Client {
   static const int PARSE_ERROR_CODE = 4000;
   static const int BINARY_MESSAGE_ERROR_CODE = 4001;
   static const int NOT_MAP_ERROR_CODE = 4002;
+  static const int ID_ERROR_CODE = 4003;
   final WebSocket socket;
 
   WebSocketClient(this.socket, VMService service) : super(service) {
     socket.listen((message) => onWebSocketMessage(message));
     socket.done.then((_) => close());
   }
 
   void onWebSocketMessage(message) {
     if (message is String) {
       var map;
       try {
         map = JSON.decode(message);
       } catch (e) {
         socket.close(PARSE_ERROR_CODE, 'Message parse error: $e');
         return;
       }
       if (map is! Map) {
         socket.close(NOT_MAP_ERROR_CODE, 'Message must be a JSON map.');
         return;
       }
       var serial = map['id'];
+      if (serial != null && serial is! num && serial is! String) {
+        socket.close(ID_ERROR_CODE, '"id" must be a number, string, or null.');
+      }
       onMessage(serial, new Message.fromJsonRpc(this, map));
     } else {
       socket.close(BINARY_MESSAGE_ERROR_CODE, 'Message must be a string.');
     }
   }
 
   void post(dynamic result) {
     try {
       socket.add(result);
     } catch (_) {
@@ skipping 160 matching lines @@
       print('Could not shutdown Observatory HTTP server:\n$e\n$st\n');
       _notifyServerState("", 0);
       return this;
     });
   }
 
 }
 
 void _notifyServerState(String ip, int port)
     native "VMServiceIO_NotifyServerState";