use symbol literals instead of const ctor in packages

pkg/polymer_expressions/lib/src/mirrors.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.
 
 library polymer_expressions.src.mirrors;
 
 import 'dart:mirrors';
 
 /**
  * Walks up the class hierarchy to find a method declaration with the given
@@ skipping 20 matching lines @@
   }
   return null;
 }
 
 /**
  * Work-around for http://dartbug.com/5794
  */
 bool hasSuperclass(ClassMirror classMirror) {
   var superclass = classMirror.superclass;
   return (superclass != null) &&
-      (superclass.qualifiedName != const Symbol('dart.core.Object'));
+      (superclass.qualifiedName != #dart.core.Object);
 }