Make String.charCodes a getter.

samples/markdown/markdown.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.
 
 /// Standalone script for parsing markdown from files and converting to HTML.
 #library('markdown_app');
 
 #import('dart:io');
 #import('lib.dart');
 
@@ skipping 24 matching lines @@
   final length = file.lengthSync();
   final buffer = new List<int>(length);
   final bytes = file.readListSync(buffer, 0, length);
   file.closeSync();
   return new String.fromCharCodes(buffer);
 }
 
 void writeFile(String path, String text) {
   final file = new File(path);
   final stream = file.openOutputStream();
-  stream.write(text.charCodes());
+  stream.write(text.charCodes);
   stream.close();
 }