Add Windows support.

lib/src/util/path_handler.dart

 // Copyright (c) 2015, 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 test.util.path_handler;
 
 import 'package:path/path.dart' as p;
 import 'package:shelf/shelf.dart' as shelf;
 
 import '../utils.dart';
@@ skipping 29 matching lines @@
       node = node.children[components[i]];
       if (node == null) break;
       if (node.handler == null) continue;
       handler = node.handler;
       handlerIndex = i;
     }
 
     if (handler == null) return new shelf.Response.notFound("Not found.");
 
     return handler(shelfChange(request,
-        path: p.joinAll(components.take(handlerIndex + 1))));
+        path: p.url.joinAll(components.take(handlerIndex + 1))));
   }
 }
 
 /// A trie node.
 class _Node {
   shelf.Handler handler;
   final children = new Map<String, _Node>();
 }