[observe] provide notifications of keys/values changed for ObservableMap

pkg/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.
 
 library observe.src.observable_map;
 
 import 'dart:collection';
 import 'package:observe/observe.dart';
 
 
@@ skipping 100 matching lines @@
     }
 
     int len = _map.length;
     V oldValue = _map[key];
 
     _map[key] = value;
 
     if (len != _map.length) {
       notifyPropertyChange(#length, len, _map.length);
       notifyChange(new MapChangeRecord.insert(key, value));
+      _notifyKeysValuesChanged();
     } else if (oldValue != value) {
       notifyChange(new MapChangeRecord(key, oldValue, value));
+      _notifyValuesChanged();
     }
   }
 
   void addAll(Map<K, V> other) {
     other.forEach((K key, V value) { this[key] = value; });
   }
 
   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.insert(key, result));
+      _notifyKeysValuesChanged();
     }
     return result;
   }
 
   V remove(Object key) {
     int len = _map.length;
     V result =  _map.remove(key);
     if (hasObservers && len != _map.length) {
       notifyChange(new MapChangeRecord.remove(key, result));
       notifyPropertyChange(#length, len, _map.length);
+      _notifyKeysValuesChanged();
     }
     return result;
   }
 
   void clear() {
     int len = _map.length;
     if (hasObservers && len > 0) {
       _map.forEach((key, value) {
         notifyChange(new MapChangeRecord.remove(key, value));
       });
       notifyPropertyChange(#length, len, 0);
+      _notifyKeysValuesChanged();
     }
     _map.clear();
   }
 
   void forEach(void f(K key, V value)) => _map.forEach(f);
 
   String toString() => Maps.mapToString(this);
+
+  // Note: we don't really have a reasonable old/new value to use here.
+  // But this should fix "keys" and "values" in templates with minimal overhead.
+  void _notifyKeysValuesChanged() {
+    notifyChange(new PropertyChangeRecord(this, #keys, null, null));
+    _notifyValuesChanged();
+  }
+
+  void _notifyValuesChanged() {
+    notifyChange(new PropertyChangeRecord(this, #values, null, null));
+  }
 }