Remove usage of dart:json.

sdk/lib/_internal/dartdoc/lib/src/json_serializer.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.
 
 /**
  * Simple library to serialize acyclic Dart types to JSON.
  * This library is not intended for broad consumption and should be replaced
  * with a more generic Dart serialization library when one is available.
  */
 library json_serializer;
 
 import 'dart:async';
+import 'dart:convert';
 import 'dart:mirrors';
-import 'dart:json' as json;
 
 String serialize(Object o) {
   var printer = new JsonPrinter();
   _serialize(null, o, printer);
   return printer.toString();
 }
 
 /// Serialize the object with pretty printing.
 String prettySerialize(Object o) {
   var printer = new JsonPrinter(prettyPrint: true);
@@ skipping 175 matching lines @@
       _sb.write('  ');
     }
   }
 
   String toString() {
     if (prettyPrint) {
       return _sb.toString();
     } else {
       // Convenient hack to remove the pretty printing this serializer adds by
       // default.
-      return json.stringify(json.parse(_sb.toString()));
+      return JSON.encode(JSON.decode(_sb.toString()));
     }
   }
 
   static int _hexDigit(int x) => x < 10 ? 48 + x : 87 + x;
 
   static void _escape(StringBuffer sb, String s) {
     final int length = s.length;
     bool needsEscape = false;
     final codeUnits = new List<int>();
     for (int i = 0; i < length; i++) {
@@ skipping 30 matching lines @@
         needsEscape = true;
         codeUnits.add(JsonPrinter.BACKSLASH);
         codeUnits.add(codeUnit);
       } else {
         codeUnits.add(codeUnit);
       }
     }
     sb.write(needsEscape ? new String.fromCharCodes(codeUnits) : s);
   }
 }