Move dart2js from sdk/lib/_internal/compiler to pkg/compiler

pkg/compiler/lib/src/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.
 
 part of dart2js.util;
 
 class Link<T> {
   T get head => throw new StateError("no elements");
   Link<T> get tail => null;
 
@@ skipping 127 matching lines @@
    */
   Link<T> toLink([Link<T> tail = const Link()]);
 
   List<T> toList();
 
   void addLast(T t);
 
   final int length;
   final bool isEmpty;
 }