Implement hashCode on objects stored in a set or used as map keys.

dart/sdk/lib/_internal/compiler/implementation/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 => null;
   Link<T> get tail => null;
 
@@ skipping 56 matching lines @@
     throw new RangeError('Index $n out of range');
   }
 
   void forEach(void f(T element)) {}
 
   bool operator ==(other) {
     if (other is !Link<T>) return false;
     return other.isEmpty;
   }
 
+  int get hashCode => throw new UnsupportedError('Link.hashCode');
+
   String toString() => "[]";
 
   get length {
     throw new UnsupportedError('get:length');
   }
 
   int slowLength() => 0;
 
   // TODO(ahe): Remove this method?
   bool contains(T element) {
@@ skipping 24 matching lines @@
    * Prepends all elements added to the builder to [tail]. The resulting list is
    * returned and the builder is cleared.
    */
   Link<T> toLink([Link<T> tail = const Link()]);
 
   void addLast(T t);
 
   final int length;
   final bool isEmpty;
 }