Drop support for old SDK and shelf versions.

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.util.one_off_handler;
 
 import 'package:path/path.dart' as p;
 import 'package:shelf/shelf.dart' as shelf;
 
-import '../utils.dart';
-
 /// A Shelf handler that provides support for one-time handlers.
 ///
 /// This is useful for handlers that only expect to be hit once before becoming
 /// invalid and don't need to have a persistent URL.
 class OneOffHandler {
   /// A map from URL paths to handlers.
   final _handlers = new Map<String, shelf.Handler>();
 
   /// The counter of handlers that have been activated.
   var _counter = 0;
 
   /// The actual [shelf.Handler] that dispatches requests.
   shelf.Handler get handler => _onRequest;
 
   /// Creates a new one-off handler that forwards to [handler].
   ///
   /// Returns a string that's the URL path for hitting this handler, relative to
   /// the URL for the one-off handler itself.
   ///
   /// [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) {
-    var components = p.url.split(shelfUrl(request).path);
+    var components = p.url.split(request.url.path);
     if (components.isEmpty) return new shelf.Response.notFound(null);
 
     var path = components.removeAt(0);
     var handler = _handlers.remove(path);
     if (handler == null) return new shelf.Response.notFound(null);
-    return handler(shelfChange(request, path: path));
+    return handler(request.change(path: path));
   }
 }