Remove usage of dart:json.

sdk/lib/_internal/pub/lib/src/utils.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.
 
 /// Generic utility functions. Stuff that should possibly be in core.
 library pub.utils;
 
 import 'dart:async';
 import 'dart:io';
-import 'dart:json' as json;
+import "dart:convert";
 import 'dart:mirrors';
 
 import "package:crypto/crypto.dart";
 import 'package:path/path.dart' as path;
 
 /// A pair of values.
 class Pair<E, F> {
   E first;
   F last;
 
@@ skipping 466 matching lines @@
       var keys = data.keys.toList();
       keys.sort((a, b) => a.toString().compareTo(b.toString()));
 
       var first = true;
       for (var key in keys) {
         if (!first) buffer.writeln();
         first = false;
 
         var keyString = key;
         if (key is! String || !_unquotableYamlString.hasMatch(key)) {
-          keyString = json.stringify(key);
+          keyString = JSON.encode(key);
         }
 
         buffer.write('$indent$keyString:');
         _stringify(true, indent, data[key]);
       }
 
       return;
     }
 
     // Everything else we just stringify using JSON to handle escapes in
     // strings and number formatting.
     var string = data;
 
     // Don't quote plain strings if not needed.
     if (data is! String || !_unquotableYamlString.hasMatch(data)) {
-      string = json.stringify(data);
+      string = JSON.encode(data);
     }
 
     if (isMapValue) {
       buffer.write(' $string');
     } else {
       buffer.write('$indent$string');
     }
   }
 
   _stringify(false, '', data);
@@ skipping 24 matching lines @@
     error is DirectoryException ||
     error is FileException ||
     error is HttpException ||
     error is HttpException ||
     error is LinkException ||
     error is OSError ||
     error is ProcessException ||
     error is SocketException ||
     error is WebSocketException;
 }