Remove usage of dart:json.

pkg/source_maps/lib/parser.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.
 
 /// Contains the top-level function to parse source maps version 3.
 library source_maps.parser;
 
-import 'dart:json' as json;
+import 'dart:convert';
 
 import 'span.dart';
 import 'src/utils.dart';
 import 'src/vlq.dart';
 
 /// Parses a source map directly from a json string.
 // TODO(sigmund): evaluate whether other maps should have the json parsed, or
 // the string represenation.
 Mapping parse(String jsonMap, {Map<String, Map> otherMaps}) =>
-  parseJson(json.parse(jsonMap), otherMaps: otherMaps);
+  parseJson(JSON.decode(jsonMap), otherMaps: otherMaps);
 
 /// Parses a source map directly from a json map object.
 Mapping parseJson(Map map, {Map<String, Map> otherMaps}) {
   if (map['version'] != 3) {
     throw new ArgumentError(
         'unexpected source map version: ${map["version"]}. '
         'Only version 3 is supported.');
   }
 
   if (!map.containsKey('file')) {
@@ skipping 352 matching lines @@
   static const _TokenKind EOF = const _TokenKind(isEof: true);
   static const _TokenKind VALUE = const _TokenKind();
   final bool isNewLine;
   final bool isNewSegment;
   final bool isEof;
   bool get isValue => !isNewLine && !isNewSegment && !isEof;
 
   const _TokenKind(
       {this.isNewLine: false, this.isNewSegment: false, this.isEof: false});
 }