Update utils to new library syntax.

utils/lib/file_system.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.
 
 // TODO(terry): Investigate common library for file I/O shared between frog and tools.
 
 /** Abstraction for file systems and utility functions to manipulate paths. */
-#library('file_system');
+library file_system;
 
 /**
  * Abstraction around file system access to work in a variety of different
  * environments.
  */
 abstract class FileSystem {
   String readAll(String filename);
 
   void writeString(String outfile, String text);
 
@@ skipping 47 matching lines @@
 String basename(String path) {
   path = canonicalizePath(path);
 
   int lastSlash = path.lastIndexOf('/', path.length);
   if (lastSlash == -1) {
     return path;
   } else {
     return path.substring(lastSlash + 1);
   }
 }