Add support for shelf 0.6.0.

lib/src/util/one_off_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.one_off_handler;
 
 import 'package:path/path.dart' as p;
 import 'package:shelf/shelf.dart' as shelf;
 
 /// A Shelf handler that provides support for one-time handlers.
@@ skipping 18 matching lines @@
   /// [handler] will be unmounted as soon as it receives a request.
   String create(shelf.Handler handler) {
     var path = _counter.toString();
     _handlers[path] = handler;
     _counter++;
     return path;
   }
 
   /// Dispatches [request] to the appropriate handler.
   _onRequest(shelf.Request request) {
-    // Skip the first component because it's always "/".
-    var components = p.url.split(request.url.path).skip(1).toList();
+    var components = p.url.split(request.url.path);
+
+    // For shelf < 0.6.0, the first component of the path is always "/". We can
+    // safely skip it.
+    if (components.isNotEmpty && components.first == "/") {
+      components.removeAt(0);
+    }
+
     if (components.isEmpty) return new shelf.Response.notFound(null);
 
     var handler = _handlers.remove(components.removeAt(0));
     if (handler == null) return new shelf.Response.notFound(null);
     return handler(request);
   }
 }