Remove usage of dart:json.

tests/standalone/vmservice/test_helper.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.
 
 library vmservice_test_helper;
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
-import 'dart:json' as JSON;
 import 'package:expect/expect.dart';
 
 abstract class VmServiceRequestHelper {
   final Uri uri;
   final HttpClient client;
 
   VmServiceRequestHelper(String url) :
       uri = Uri.parse(url),
       client = new HttpClient();
 
@@ skipping 17 matching lines @@
     var replyAsString;
     try {
       replyAsString = UTF8.decode(data);
     } catch (e) {
       onRequestFailed(e);
       return;
     }
     print('** Response: $replyAsString');
     var reply;
     try {
-      reply = JSON.parse(replyAsString);
+      reply = JSON.decode(replyAsString);
     } catch (e) {
       onRequestFailed(e);
       return;
     }
     if (reply is! Map) {
       onRequestFailed('Reply was not a map: $reply');
       return;
     }
     if (reply['type'] == null) {
       onRequestFailed('Reply does not contain a type key: $reply');
@@ skipping 114 matching lines @@
       if (isolate['id'] == id) {
         exists = true;
         Expect.isTrue(isolate['name'].startsWith(name),
                       'Isolate $id does not have name prefix: $name'
                       ' (was ${isolate['name']})');
       }
     });
     Expect.isTrue(exists, 'No isolate with id: $id');
   }
 }