Extract an http_parser package from shelf.

pkg/http_parser/test/http_date_test.dart

Index: pkg/http_parser/test/http_date_test.dart
diff --git a/pkg/shelf/test/http_date_test.dart b/pkg/http_parser/test/http_date_test.dart
similarity index 99%
rename from pkg/shelf/test/http_date_test.dart
rename to pkg/http_parser/test/http_date_test.dart
index 4af874f9014ec2d0271875463809284705b2ca47..680147a08761dc14bb82e9f14ecff1d13774fb63 100644
--- a/pkg/shelf/test/http_date_test.dart
+++ b/pkg/http_parser/test/http_date_test.dart
@@ -2,9 +2,9 @@
 // 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() {