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

dart/sdk/lib/_internal/compiler/implementation/util/link_implementation.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 util_implementation;
 
 class LinkIterator<T> implements Iterator<T> {
   T _current;
   Link<T> _link;
 
@@ skipping 82 matching lines @@
     while (!myElements.isEmpty && !other.isEmpty) {
       if (myElements.head != other.head) {
         return false;
       }
       myElements = myElements.tail;
       other = other.tail;
     }
     return myElements.isEmpty && other.isEmpty;
   }
 
+  int get hashCode => throw new UnsupportedError('LinkEntry.hashCode');
+
   int slowLength() => 1 + tail.slowLength();
 }
 
 class LinkBuilderImplementation<T> implements LinkBuilder<T> {
   LinkEntry<T> head = null;
   LinkEntry<T> lastLink = null;
   int length = 0;
 
   LinkBuilderImplementation();
 
@@ skipping 12 matching lines @@
     if (head == null) {
       head = entry;
     } else {
       lastLink.tail = entry;
     }
     lastLink = entry;
   }
 
   bool get isEmpty => length == 0;
 }