Remove usage of dart:json.

pkg/http_server/lib/src/http_body_impl.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 http_server;
 
 class _HttpBodyHandlerTransformer
     extends StreamEventTransformer<HttpRequest, HttpRequestBody> {
   final Encoding _defaultEncoding;
   _HttpBodyHandlerTransformer(this._defaultEncoding);
@@ skipping 97 matching lines @@
     switch (contentType.primaryType) {
       case "text":
         return asText(ASCII);
 
       case "application":
         switch (contentType.subType) {
           case "json":
             return asText(UTF8)
                 .then((body) => new _HttpBody(contentType,
                                               "json",
-                                              JSON.parse(body.body)));
+                                              JSON.decode(body.body)));
 
           case "x-www-form-urlencoded":
             return asText(ASCII)
                 .then((body) {
                   var map = Uri.splitQueryString(body.body,
                       decode: (s) => defaultEncoding.decode(s));
                   var result = {};
                   for (var key in map.keys) {
                     result[key] = map[key];
                   }
@@ skipping 61 matching lines @@
   _HttpClientResponseBody(HttpClientResponse response, HttpBody body)
       : super(body.contentType, body.type, body.body),
         this.response = response;
 
   int get statusCode => response.statusCode;
 
   String get reasonPhrase => response.reasonPhrase;
 
   HttpHeaders get headers => response.headers;
 }