Allow Object when doing lookups.

pkg/mdv_observe/lib/src/observable_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 mdv_observe;
 
 // TODO(jmesserly): this needs to be faster. We currently require multiple
 // lookups per key to get the old value.
 // TODO(jmesserly): this doesn't implement the precise interfaces like
 // LinkedHashMap, SplayTreeMap or HashMap. However it can use them for the
@@ skipping 76 matching lines @@
   Iterable<K> get keys => _map.keys;
 
   Iterable<V> get values => _map.values;
 
   int get length =>_map.length;
 
   bool get isEmpty => length == 0;
 
   bool get isNotEmpty => !isEmpty;
 
-  bool containsValue(V value) => _map.containsValue(value);
+  bool containsValue(Object value) => _map.containsValue(value);
 
-  bool containsKey(K key) => _map.containsKey(key);
+  bool containsKey(Object key) => _map.containsKey(key);
 
-  V operator [](K key) => _map[key];
+  V operator [](Object key) => _map[key];
 
   void operator []=(K key, V value) {
     int len = _map.length;
     V oldValue = _map[key];
     _map[key] = value;
     if (hasObservers) {
       if (len != _map.length) {
         notifyPropertyChange(_LENGTH, len, _map.length);
         notifyChange(new MapChangeRecord(key, isInsert: true));
       } else if (!identical(oldValue, value)) {
         notifyChange(new MapChangeRecord(key));
       }
     }
   }
 
   V putIfAbsent(K key, V ifAbsent()) {
     int len = _map.length;
     V result = _map.putIfAbsent(key, ifAbsent);
     if (hasObservers && len != _map.length) {
       notifyPropertyChange(_LENGTH, len, _map.length);
       notifyChange(new MapChangeRecord(key, isInsert: true));
     }
     return result;
   }
 
-  V remove(K key) {
+  V remove(Object key) {
     int len = _map.length;
     V result =  _map.remove(key);
     if (hasObservers && len != _map.length) {
       notifyChange(new MapChangeRecord(key, isRemove: true));
       notifyPropertyChange(_LENGTH, len, _map.length);
     }
     return result;
   }
 
   void clear() {
     int len = _map.length;
     if (hasObservers && len > 0) {
       _map.forEach((key, value) {
         notifyChange(new MapChangeRecord(key, isRemove: true));
       });
       notifyPropertyChange(_LENGTH, len, 0);
     }
     _map.clear();
   }
 
   void forEach(void f(K key, V value)) => _map.forEach(f);
 
   String toString() => Maps.mapToString(this);
 }