Stop using the Hashable interface.

lib/coreimpl/linked_hash_map.dart

 // Copyright (c) 2012, 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.
 
 /**
  * This class represents a pair of two objects, used by LinkedHashMap
  * to store a {key, value} in a list.
  */
 class KeyValuePair<K, V> {
   KeyValuePair(this.key, this.value) {}
 
   final K key;
   V value;
 }
 
 /**
  * A LinkedHashMap is a hash map that preserves the insertion order
  * when iterating over the keys or the values. Updating the value of a
  * key does not change the order.
  */
-class LinkedHashMapImplementation<K extends Hashable, V>
+class LinkedHashMapImplementation<K, V>
     implements LinkedHashMap<K, V> {
   DoubleLinkedQueue<KeyValuePair<K, V>> _list;
   HashMap<K, DoubleLinkedQueueEntry<KeyValuePair<K, V>>> _map;
 
   LinkedHashMapImplementation() {
     _map = new HashMap<K, DoubleLinkedQueueEntry<KeyValuePair<K, V>>>();
     _list = new DoubleLinkedQueue<KeyValuePair<K, V>>();
   }
 
   factory LinkedHashMapImplementation.from(Map<K, V> other) {
@@ skipping 80 matching lines @@
 
   void clear() {
     _map.clear();
     _list.clear();
   }
 
   String toString() {
     return Maps.mapToString(this);
   }
 }