Revert "Don't use `LinkedList` in the core libraries anymore."

tests/corelib/reg_exp_cache_test.dart

-// Copyright (c) 2017, 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.
-
-// Runs several similar regexps in a loop to see if an internal cache works (at
-// least in easy conditions).
-
-import "package:expect/expect.dart";
-
-void main() {
-  for (int j = 1; j < 50; j++) {
-    for (int i = 0; i < 20 * j; i++) {
-      var regExp = new RegExp("foo$i");
-      var match = regExp.firstMatch("foo$i");
-      Expect.isNotNull(match);
-      Expect.equals("foo$i", match[0]);
-    }
-  }
-}