Remove usage of dart:json.

tests/html/xhr_test.dart

 // Copyright (c) 2012, 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 XHRTest;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_individual_config.dart';
 import 'dart:async';
 import 'dart:html';
-import 'dart:json' as json;
+import "dart:convert";
 import 'dart:typed_data';
 
 void fail(message) {
   guardAsync(() {
     expect(false, isTrue, reason: message);
   });
 }
 
 main() {
   useHtmlIndividualConfiguration();
   // Cache blocker is a workaround for:
   // https://code.google.com/p/dart/issues/detail?id=11834
   var cacheBlocker = new DateTime.now().millisecondsSinceEpoch;
   var url = '/root_dart/tests/html/xhr_cross_origin_data.txt?'
       'cacheBlock=$cacheBlocker';
 
   void validate200Response(xhr) {
     expect(xhr.status, equals(200));
-    var data = json.parse(xhr.responseText);
+    var data = JSON.decode(xhr.responseText);
     expect(data, contains('feed'));
     expect(data['feed'], contains('entry'));
     expect(data, isMap);
   }
 
   void validate404(xhr) {
     expect(xhr.status, equals(404));
     expect(xhr.responseText, equals(''));
   }
 
@@ skipping 195 matching lines @@
           (xhr) {
             expect(xhr.status, equals(200));
             var blob = xhr.response;
             expect(blob is Blob, isTrue);
             expect(blob, isNotNull);
           });
       }
     });
   });
 }