Add parseJson to DartUtilities.

tools/dom/src/html_native_DOMImplementation.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.
 
 part of html;
 
 class _Property {
   _Property(this.name) :
       _hasValue = false,
       writable = false,
@@ skipping 144 matching lines @@
       result[list[i]] = list[i + 1];
     }
   }
 
   static bool isMap(obj) => obj is Map;
 
   static List toListIfIterable(obj) => obj is Iterable ? obj.toList() : null;
 
   static Map createMap() => {};
 
+  static parseJson(String jsonSource) => const JsonDecoder().convert(jsonSource);
+
   static makeUnimplementedError(String fileName, int lineNo) {
     return new UnsupportedError('[info: $fileName:$lineNo]');
   }
 
   static bool isTypeSubclassOf(Type type, Type other) {
     if (type == other) {
       return true;
     }
     var superclass = reflectClass(type).superclass;
     if (superclass != null) {
@@ skipping 806 matching lines @@
   _scheduleImmediateHelper._schedule(callback);
 };
 
 get _pureIsolateScheduleImmediateClosure => ((void callback()) =>
   throw new UnimplementedError("scheduleMicrotask in background isolates "
                                "are not supported in the browser"));
 
 void _initializeCustomElement(Element e) {
   _Utils.initializeCustomElement(e);
 }