Allow Object when doing lookups.

tests/html/custom_element_bindings_test.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.
 
 library custom_element_bindings_test;
 
 import 'dart:async';
 import 'dart:html';
 import 'package:mdv_observe/mdv_observe.dart';
 import 'package:unittest/html_config.dart';
@@ skipping 243 matching lines @@
   void unbindAll() => real.unbindAll();
 }
 
 // TODO(jmesserly): would be nice to use mocks when mirrors work on dart2js.
 class AttributeMapWrapper<K, V> implements Map<K, V> {
   final List log = [];
   Map<K, V> _map;
 
   AttributeMapWrapper(this._map);
 
-  bool containsValue(V value) => _map.containsValue(value);
-  bool containsKey(K key) => _map.containsKey(key);
-  V operator [](K key) => _map[key];
+  bool containsValue(Object value) => _map.containsValue(value);
+  bool containsKey(Object key) => _map.containsKey(key);
+  V operator [](Object key) => _map[key];
 
   void operator []=(K key, V value) {
     log.add(['[]=', key, value]);
     _map[key] = value;
   }
 
   V putIfAbsent(K key, V ifAbsent()) => _map.putIfAbsent(key, ifAbsent);
 
-  V remove(K key) {
+  V remove(Object key) {
     log.add(['remove', key]);
     _map.remove(key);
   }
 
   void clear() => _map.clear();
   void forEach(void f(K key, V value)) => _map.forEach(f);
   Iterable<K> get keys => _map.keys;
   Iterable<V> get values => _map.values;
   int get length => _map.length;
   bool get isEmpty => _map.isEmpty;
   bool get isNotEmpty => _map.isNotEmpty;
 }