Remove usage of dart:json.

sdk/lib/_internal/compiler/samples/jsonify/jsonify.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.
 
 import 'dart:io';
-import 'dart:json';
+import 'dart:convert';
 
 // TODO(ahe): Should be dart:mirrors.
 import '../../implementation/mirrors/mirrors.dart';
 
 import '../../../libraries.dart'
     show LIBRARIES, LibraryInfo;
 
 import '../../implementation/mirrors/dart2js_mirror.dart'
     show analyze, BackDoor;
 
@@ skipping 68 matching lines @@
 // 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.
 
 // DO NOT EDIT.
 // This file is generated by jsonify.dart.
 
 library dart.sdk_sources;
 
 const Map<String, String> SDK_SOURCES = const <String, String>''');
-  output.writeStringSync(stringify(map).replaceAll(r'$', r'\$'));
+  output.writeStringSync(JSON.encode(map).replaceAll(r'$', r'\$'));
   output.writeStringSync(';\n');
   output.closeSync();
 }