Move frog/leg to lib/compiler/implementation.

frog/leg/util/link.dart

-// Copyright (c) 2011, 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.
-
-interface Link<T> extends Iterable<T> default LinkFactory<T> {
-  final T head;
-  final Link<T> tail;
-
-  Link(T head, [Link<T> tail]);
-  Link.fromList(List<T> list);
-
-  Link<T> prepend(T element);
-  List<T> toList();
-  bool isEmpty();
-  Link<T> reverse();
-  Link<T> reversePrependAll(Link<T> from);
-
-  void printOn(StringBuffer buffer, [separatedBy]);
-
-  void forEach(void f(T element));
-}
-
-interface EmptyLink<T> extends Link<T> default LinkTail<T> {
-  const EmptyLink();
-}
-
-interface LinkBuilder<T> default LinkBuilderImplementation<T> {
-  LinkBuilder();
-
-  Link<T> toLink();
-  void addLast(T t);
-
-  final int length;
-}