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

sdk/lib/internal/linked_list.dart

Index: sdk/lib/internal/linked_list.dart
diff --git a/sdk/lib/internal/linked_list.dart b/sdk/lib/internal/linked_list.dart
deleted file mode 100644
index a63bed150f261d8eebd2b3fcfb6618c266d1953f..0000000000000000000000000000000000000000
--- a/sdk/lib/internal/linked_list.dart
+++ /dev/null
@@ -1,123 +0,0 @@
-// 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.
-
-part of dart._internal;
-
-/// A rudimentary linked list.
-class LinkedList<T extends LinkedListEntry<T>> extends IterableBase<T> {
-  T first;
-  T last;
-  int length = 0;
-
-  bool get isEmpty => length == 0;
-
-  /**
-   * Adds [newLast] to the end of this linked list.
-   */
-  void add(T newLast) {
-    assert(newLast._next == null && newLast._previous == null);
-    if (last != null) {
-      assert(last._next == null);
-      last._next = newLast;
-    } else {
-      first = newLast;
-    }
-    newLast._previous = last;
-    last = newLast;
-    last._list = this;
-    length++;
-  }
-
-  /**
-   * Adds [newFirst] to the beginning of this linked list.
-   */
-  void addFirst(T newFirst) {
-    if (first != null) {
-      assert(first._previous == null);
-      first._previous = newFirst;
-    } else {
-      last = newFirst;
-    }
-    newFirst._next = first;
-    first = newFirst;
-    first._list = this;
-    length++;
-  }
-
-  /**
-   * Removes the given [node] from this list.
-   *
-   * The entry must be in this linked list when this method is called. Also see
-   * [LinkedListEntry.unlink].
-   */
-  void remove(T node) {
-    assert(node._previous != null || node._next != null || length == 1);
-    length--;
-    if (node._previous == null) {
-      assert(identical(node, first));
-      first = node._next;
-    } else {
-      node._previous._next = node._next;
-    }
-    if (node._next == null) {
-      assert(identical(node, last));
-      last = node._previous;
-    } else {
-      node._next._previous = node._previous;
-    }
-    node._next = node._previous = null;
-  }
-
-  Iterator<T> get iterator => new _LinkedListIterator<T>(this);
-}
-
-class LinkedListEntry<T extends LinkedListEntry<T>> {
-  T _next;
-  T _previous;
-  LinkedList<T> _list;
-
-  /**
-   * Unlinks the element from its linked list.
-   *
-   * The entry must be in a linked list when this method is called.
-   * This is equivalent to calling [LinkedList.remove] on the list this entry
-   * is currently in.
-   */
-  void unlink() {
-    _list.remove(this);
-  }
-}
-
-class _LinkedListIterator<T extends LinkedListEntry<T>> implements Iterator<T> {
-  /// The current element of the iterator.
-  // This field is writeable, but should only read by users of this class.
-  T current;
-
-  /// The list the iterator iterates over.
-  ///
-  /// Set to [null] if the provided list was empty (indicating that there were
-  /// no entries to iterate over).
-  ///
-  /// Set to [null] as soon as [moveNext] was invoked (indicating that the
-  /// iterator has to work with [current] from now on.
-  LinkedList<T> _list;
-
-  _LinkedListIterator(this._list) {
-    if (_list.length == 0) _list = null;
-  }
-
-  bool moveNext() {
-    // current is null if the iterator hasn't started iterating, or if the
-    // iteration is finished. In the first case, the [_list] field is not null.
-    if (current == null) {
-      if (_list == null) return false;
-      assert(_list.length > 0);
-      current = _list.first;
-      _list = null;
-      return true;
-    }
-    current = current._next;
-    return current != null;
-  }
-}