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

sdk/lib/io/io.dart

 // Copyright (c) 2012, 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.
 
 /**
  * File, socket, HTTP, and other I/O support for server applications.
  *
  * The I/O library is used for Dart server applications,
  * which run on a stand-alone Dart VM from the command line.
  * *This library does not work in browser-based applications.*
@@ skipping 179 matching lines @@
  * tour](https://www.dartlang.org/docs/dart-up-and-running/ch03.html#dartio---io-for-command-line-apps).
  *
  * To learn more about I/O in Dart, refer to the [tutorial about writing
  * command-line apps](https://www.dartlang.org/docs/tutorials/cmdline/).
  */
 library dart.io;
 
 import 'dart:async';
 import 'dart:_internal' hide Symbol;
 import 'dart:collection'
-    show
-        HashMap,
-        HashSet,
-        Queue,
-        ListQueue,
-        LinkedList,
-        LinkedListEntry,
-        UnmodifiableMapView;
+    show HashMap, HashSet, Queue, ListQueue, UnmodifiableMapView;
 import 'dart:convert';
 import 'dart:developer' hide log;
 import 'dart:isolate';
 import 'dart:math';
 import 'dart:typed_data';
 import 'dart:nativewrappers';
 
 part 'bytes_builder.dart';
 part 'common.dart';
 part 'crypto.dart';
@@ skipping 20 matching lines @@
 part 'secure_server_socket.dart';
 part 'secure_socket.dart';
 part 'security_context.dart';
 part 'service_object.dart';
 part 'socket.dart';
 part 'stdio.dart';
 part 'string_transformer.dart';
 part 'sync_socket.dart';
 part 'websocket.dart';
 part 'websocket_impl.dart';