Allow trailing / in directory paths

tools/testing/dart/legacy_path.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.
 
 part of utils;
 
 class Path {
   final String _path;
   final bool isWindowsShare;
 
   Path(String source)
       : _path = _clean(source), isWindowsShare = _isWindowsShare(source);
 
   Path.raw(String source) : _path = source, isWindowsShare = false;
 
   Path._internal(String this._path, bool this.isWindowsShare);
 
   static String _clean(String source) {
     if (Platform.operatingSystem == 'windows') return _cleanWindows(source);
+    // Remove trailing slash from directories:
+    if (source.length > 1 && source.endsWith('/')) {
+      return source.substring(0, source.length - 1);
+    }
     return source;
   }
 
   static String _cleanWindows(String source) {
     // Change \ to /.
     var clean = source.replaceAll('\\', '/');
     // Add / before intial [Drive letter]:
     if (clean.length >= 2 && clean[1] == ':') {
       clean = '/$clean';
     }
@@ skipping 270 matching lines @@
     while (pos > 0 && _path[pos - 1] == '/') --pos;
     var dirPath = (pos > 0) ? _path.substring(0, pos) : '/';
     return new Path._internal(dirPath, isWindowsShare);
   }
 
   String get filename {
     int pos = _path.lastIndexOf('/');
     return _path.substring(pos + 1);
   }
 }