Changed interfaces to abstract classes in utils.

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');
 
 /**
  * Abstraction around file system access to work in a variety of different
  * environments.
  */
-interface FileSystem {
+abstract class FileSystem {
   String readAll(String filename);
 
   void writeString(String outfile, String text);
 
   bool fileExists(String filename);
 
   void createDirectory(String path, [bool recursive]);
   void removeDirectory(String path, [bool recursive]);
 }
 
-/** 
- * Replaces all back slashes (\) with forward slashes (/) in [path] and 
+/**
+ * Replaces all back slashes (\) with forward slashes (/) in [path] and
  * return the result.
  */
 String canonicalizePath(String path) {
   return path.replaceAll('\\', '/');
 }
 
 /** Join [path1] to [path2]. */
 String joinPaths(String path1, String path2) {
   path1 = canonicalizePath(path1);
   path2 = canonicalizePath(path2);
@@ skipping 29 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);
   }
 }