Remove usage of dart:json.

pkg/yaml/lib/yaml.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.
 
 /// A parser for [YAML](http://www.yaml.org/).
 ///
 /// ## Installing ##
 ///
 /// Use [pub][] to install this package. Add the following to your
 /// `pubspec.yaml` file.
@@ skipping 11 matching lines @@
 /// Use [loadYaml] to load a single document, or [loadYamlStream] to load a
 /// stream of documents. For example:
 ///
 ///     import 'package:yaml/yaml.dart';
 ///     main() {
 ///       var doc = loadYaml("YAML: YAML Ain't Markup Language");
 ///       print(doc['YAML']);
 ///     }
 ///
 /// This library currently doesn't support dumping to YAML. You should use
-/// `stringify` from `dart:json` instead:
+/// `JSON.encode` from `dart:convert` instead:
 ///
-///     import 'dart:json' as json;
+///     import 'dart:convert';
 ///     import 'package:yaml/yaml.dart';
 ///     main() {
 ///       var doc = loadYaml("YAML: YAML Ain't Markup Language");
-///       print(json.stringify(doc));
+///       print(JSON.encode(doc));
 ///     }
 ///
 /// [pub]: http://pub.dartlang.org
 /// [pkg]: http://pub.dartlang.org/packages/yaml
 library yaml;
 
 import 'src/composer.dart';
 import 'src/constructor.dart';
 import 'src/parser.dart';
 import 'src/yaml_exception.dart';
@@ skipping 22 matching lines @@
 /// The return value is mostly normal Dart objects. However, since YAML mappings
 /// support some key types that the default Dart map implementation doesn't
 /// (null, NaN, booleans, lists, and maps), all maps in the returned document
 /// are [YamlMap]s. These have a few small behavioral differences from the
 /// default Map implementation; for details, see the [YamlMap] class.
 List loadYamlStream(String yaml) {
   return new Parser(yaml).l_yamlStream()
       .map((doc) => new Constructor(new Composer(doc).compose()).construct())
       .toList();
 }