Remove usage of dart:json.

runtime/bin/vmservice/running_isolates.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 RunningIsolates implements ServiceRequestRouter {
   final Map<int, RunningIsolate> isolates = new Map<int, RunningIsolate>();
 
   RunningIsolates();
@@ skipping 17 matching lines @@
     var members = [];
     var result = {};
     isolates.forEach((sp, ri) {
       members.add({
         'id': sp,
         'name': ri.name
         });
     });
     result['type'] = 'IsolateList';
     result['members'] = members;
-    request.setResponse(JSON.stringify(result));
+    request.setResponse(JSON.encode(result));
   }
 
   Future route(ServiceRequest request) {
     if (request.pathSegments.length == 0) {
       return null;
     }
     if (request.pathSegments[0] != 'isolates') {
       return null;
     }
     if (request.pathSegments.length == 1) {
@@ skipping 16 matching lines @@
     // Consume '/isolates/isolateId'
     request.pathSegments.removeRange(0, 2);
     if (request.pathSegments.length == 0) {
       // The request is now empty.
       request.setErrorResponse('No request for isolate: /isolates/$isolateId');
       return new Future.value(request);
     }
     return isolate.route(request);
   }
 }