pkg/shelf: added `url` and `scriptName` named params to Request.change

pkg/shelf/lib/src/shelf_unmodifiable_map.dart

 // Copyright (c) 2014, 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 shelf.shelf_unmodifiable_map;
 
 import 'dart:collection';
 
-// TODO(kevmoo): use UnmodifiableMapView from SDK once 1.4 ships
+// TODO(kevmoo): MapView lacks a const ctor, so we have to use DelegatingMap
+// from pkg/collection - https://codereview.chromium.org/294093003/
 import 'package:collection/wrappers.dart' as pc;
 
 /// A simple wrapper over [pc.UnmodifiableMapView] which avoids re-wrapping
 /// itself.
-class ShelfUnmodifiableMap<V> extends pc.UnmodifiableMapView<String, V> {
+class ShelfUnmodifiableMap<V> extends UnmodifiableMapView<String, V> {
   /// If [source] is a [ShelfUnmodifiableMap] with matching [ignoreKeyCase],
   /// then [source] is returned.
   ///
   /// If [source] is `null` it is treated like an empty map.
   ///
   /// If [ignoreKeyCase] is `true`, the keys will have case-insensitive access.
   ///
   /// [source] is copied to a new [Map] to ensure changes to the paramater value
   /// after constructions are not reflected.
   factory ShelfUnmodifiableMap(Map<String, V> source,
@@ skipping 24 matching lines @@
   }
 
   ShelfUnmodifiableMap._(Map<String, V> source) : super(source);
 }
 
 /// An const empty implementation of [ShelfUnmodifiableMap].
 class _EmptyShelfUnmodifiableMap<V> extends pc.DelegatingMap<String, V>
     implements ShelfUnmodifiableMap<V>  {
   const _EmptyShelfUnmodifiableMap() : super(const {});
 }