Extract an http_parser package from shelf.

pkg/shelf/lib/src/response.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.response;
 
 import 'dart:async';
 import 'dart:convert';
 
 import 'package:collection/wrappers.dart';
+import 'package:http_parser/http_parser.dart';
 
-import 'media_type.dart';
 import 'message.dart';
-import 'util.dart';
 
 /// The response returned by a [Handler].
 class Response extends Message {
   /// The HTTP status code of the response.
   final int statusCode;
 
   /// The date and time after which the response's data should be considered
   /// stale.
   ///
   /// This is parsed from the Expires header in [headers]. If [headers] doesn't
@@ skipping 239 matching lines @@
 /// Converts [location], which may be a [String] or a [Uri], to a [String].
 ///
 /// Throws an [ArgumentError] if [location] isn't a [String] or a [Uri].
 String _locationToString(location) {
   if (location is String) return location;
   if (location is Uri) return location.toString();
 
   throw new ArgumentError('Response location must be a String or Uri, was '
       '"$location".');
 }