Allow Object when doing lookups.

sdk/lib/collection/linked_hash_map.dart

 // Copyright (c) 2013, 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 dart.collection;
 
 /**
  * A hash-table based implementation of [Map].
  *
  * Keys insertion order is remembered, and keys are iterated in insertion order.
  * Values are iterated in their corresponding key's order.
  *
  * The keys of a `HashMap` must have consistent [Object.operator==]
  * and [Object.hashCode] implementations. This means that the `==` operator
  * must define a stable equivalence relation on the keys (reflexive,
  * anti-symmetric, transitive, and consistent over time), and that `hashCode`
  * must be the same for objects that are considered equal by `==`.
  *
  * The map allows `null` as a key.
  */
 class LinkedHashMap<K, V> implements Map<K, V> {
   external LinkedHashMap();
 
   factory LinkedHashMap.from(Map<K, V> other) {
     return new LinkedHashMap<K, V>()..addAll(other);
   }
 
-  external bool containsKey(K key);
+  external bool containsKey(Object key);
 
-  external bool containsValue(V value);
+  external bool containsValue(Object value);
 
   external void addAll(Map<K, V> other);
 
-  external V operator [](K key);
+  external V operator [](Object key);
 
   external void operator []=(K key, V value);
 
   external V putIfAbsent(K key, V ifAbsent());
 
-  external V remove(K key);
+  external V remove(Object key);
 
   external void clear();
 
   external void forEach(void action (K key, V value));
 
   /** The keys of the map, in insertion order. */
   external Iterable<K> get keys;
   /** The values of the map, in the order of their corresponding [keys].*/
   external Iterable<V> get values;
 
   external int get length;
 
   external bool get isEmpty;
 
   external bool get isNotEmpty;
 
   String toString() => Maps.mapToString(this);
 }