Remove usage of dart:json.

sdk/lib/_internal/compiler/samples/jsonify/jsonify.dart

Index: sdk/lib/_internal/compiler/samples/jsonify/jsonify.dart
diff --git a/sdk/lib/_internal/compiler/samples/jsonify/jsonify.dart b/sdk/lib/_internal/compiler/samples/jsonify/jsonify.dart
index 82232c9788c4dd4af5e5b7b01eef5d458f3cde15..931e24b97d19ac2301bc7497efd77bf56a8e272e 100644
--- a/sdk/lib/_internal/compiler/samples/jsonify/jsonify.dart
+++ b/sdk/lib/_internal/compiler/samples/jsonify/jsonify.dart
@@ -3,7 +3,7 @@
 // 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';
@@ -92,7 +92,7 @@ jsonify(MirrorSystem mirrors) {
 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();
 }