Allow Object when doing lookups.

tests/html/custom_element_bindings_test.dart

Index: tests/html/custom_element_bindings_test.dart
diff --git a/tests/html/custom_element_bindings_test.dart b/tests/html/custom_element_bindings_test.dart
index 3b9d6a9262fea8fa23966766e76e694b94f885c1..6548a7f908ac9eaf395dcfddf425cc3f98e2d71b 100644
--- a/tests/html/custom_element_bindings_test.dart
+++ b/tests/html/custom_element_bindings_test.dart
@@ -261,9 +261,9 @@ class AttributeMapWrapper<K, V> implements Map<K, V> {
 
   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]);
@@ -272,7 +272,7 @@ class AttributeMapWrapper<K, V> implements Map<K, V> {
 
   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);
   }