Revert "Switch libraries to using new tags."

sdk/lib/json/json.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.
 
-library dart.json;
+#library("dart:json");
 
-import 'dart:math';
+#import('dart:math');
 
 // JSON parsing and serialization.
 
 /**
  * Error thrown by JSON serialization if an object cannot be serialized.
  *
  * The [unsupportedObject] field holds that object that failed to be serialized.
  *
  * If an isn't directly serializable, the serializer calls the 'toJson' method
  * on the object. If that call fails, the error will be stored in the [cause]
@@ skipping 575 matching lines @@
         first = false;
       });
       sb.add('}');
       seen.removeLast();
       return true;
     } else {
       return false;
     }
   }
 }