Stop using the Hashable interface.

lib/core/map.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.
 
 /**
  * A [Map] is an associative container, mapping a key to a value.
  * Null values are supported, but null keys are not.
  */
-interface Map<K, V> default HashMapImplementation<K extends Hashable, V> {
+interface Map<K, V> default HashMapImplementation<K, V> {
   /**
    * Creates a map with the default implementation.
    */
   Map();
 
   /**
    * Creates a [Map] that contains all key value pairs of [other].
    */
   Map.from(Map<K, V> other);
 
@@ skipping 65 matching lines @@
    * Returns true if there is no {key, value} pair in the map.
    */
   bool isEmpty();
 }
 
 /**
  * Hash map version of the [Map] interface. A [HashMap] does not
  * provide any guarantees on the order of keys and values in [getKeys]
  * and [getValues].
  */
-interface HashMap<K extends Hashable, V> extends Map<K, V>
-    default HashMapImplementation<K extends Hashable, V> {
+interface HashMap<K, V> extends Map<K, V>
+    default HashMapImplementation<K, V> {
   /**
    * Creates a map with the default implementation.
    */
   HashMap();
 
   /**
    * Creates a [HashMap] that contains all key value pairs of [other].
    */
   HashMap.from(Map<K, V> other);
 }
 
 /**
  * Hash map version of the [Map] interface that preserves insertion
  * order.
  */
-interface LinkedHashMap<K extends Hashable, V> extends HashMap<K, V>
-    default LinkedHashMapImplementation<K extends Hashable, V> {
+interface LinkedHashMap<K, V> extends HashMap<K, V>
+    default LinkedHashMapImplementation<K, V> {
   /**
    * Creates a map with the default implementation.
    */
   LinkedHashMap();
 
   /**
    * Creates a [LinkedHashMap] that contains all key value pairs of [other].
    */
   LinkedHashMap.from(Map<K, V> other);
 }