Extract an http_parser package from shelf.

pkg/http_parser/test/http_date_test.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.http_date_test;
+library http_parser.http_date_test;
 
-import 'package:shelf/src/util.dart';
+import 'package:http_parser/http_parser.dart';
 import 'package:unittest/unittest.dart';
 
 void main() {
   group("parse", () {
     group("RFC 1123", () {
       test("parses the example date", () {
         var date = parseHttpDate("Sun, 06 Nov 1994 08:49:37 GMT");
         expect(date.day, equals(6));
         expect(date.month, equals(DateTime.NOVEMBER));
         expect(date.year, equals(1994));
@@ skipping 288 matching lines @@
             throwsFormatException);
       });
 
       test("disallows trailing whitespace", () {
         expect(() => parseHttpDate("Sun November 0 08:49:37 1994 "),
             throwsFormatException);
       });
     });
   });
 }