Stop using the Hashable interface.

lib/coreimpl/hash_map_set.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.
 
 // Hash map implementation with open addressing and quadratic probing.
-class HashMapImplementation<K extends Hashable, V> implements HashMap<K, V> {
+class HashMapImplementation<K, V> implements HashMap<K, V> {
 
   // The [_keys] list contains the keys inserted in the map.
   // The [_keys] list must be a raw list because it
   // will contain both elements of type K, and the [_DELETED_KEY] of type
   // [_DeletedKeySentinel].
   // The alternative of declaring the [_keys] list as of type Object
   // does not work, because the HashSetIterator constructor would fail:
   //  HashSetIterator(HashSet<E> set)
   //    : _nextValidIndex = -1,
   //      _entries = set_._backingMap._keys {
@@ skipping 252 matching lines @@
       }
     }
     return false;
   }
 
   String toString() {
     return Maps.mapToString(this);
   }
 }
 
-class HashSetImplementation<E extends Hashable> implements HashSet<E> {
+class HashSetImplementation<E > implements HashSet<E> {
 
   HashSetImplementation() {
     _backingMap = new HashMapImplementation<E, E>();
   }
 
   factory HashSetImplementation.from(Iterable<E> other) {
     Set<E> set = new HashSetImplementation<E>();
     for (final e in other) {
       set.add(e);
     }
@@ skipping 157 matching lines @@
 
 /**
  * A singleton sentinel used to represent when a key is deleted from the map.
  * We can't use [: const Object() :] as a sentinel because it would end up
  * canonicalized and then we cannot distinguish the deleted key from the
  * canonicalized [: Object() :].
  */
 class _DeletedKeySentinel {
   const _DeletedKeySentinel();
 }