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

runtime/lib/core_patch.dart

 // Copyright (c) 2013, 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.
 
 import "dart:async";
+import "dart:collection" show LinkedList, LinkedListEntry;
 import 'dart:convert' show ASCII, JSON;
 import "dart:isolate";
 import "dart:math";
 import "dart:typed_data";
 import 'dart:_internal' as internal;
 
 // The members of this class are cloned and added to each class that
 // represents an enum type.
 class _EnumHelper {
   String _name;
@@ skipping 57 matching lines @@
       return true;
     }
   }
 }
 
 @patch
 class StackTrace {
   @patch
   static StackTrace get current native "StackTrace_current";
 }