[dart:_http] Fix http_cookie_date_test.dart compile errors.

Fixes dart-lang/sdk#28843
Change-Id: I544f9d13e68a41412b0a7dd00b7a6d20ce3ef99e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/91222
Commit-Queue: Jonas Termansen <[email protected]>
Reviewed-by: William Hesse <[email protected]>

Author: sortie

tests/standalone_2/io/http_cookie_date_test.dart

@@ -2,14 +2,12 @@
 // 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 dart.http;
+library dart._http;
 
 import "dart:async";
 import "dart:collection";
 import "dart:convert";
-import "dart:developer";
 import "dart:io";
-import "dart:isolate";
 import "dart:math";
 import "dart:typed_data";
 import "package:expect/expect.dart";