add custom_element package

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.
 
 part of 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 49 matching lines @@
   /**
    * Creates an observable map that contains all key value pairs of [other].
    * It will attempt to use the same backing map type if the other map is a
    * [LinkedHashMap], [SplayTreeMap], or [HashMap]. Otherwise it defaults to
    * [HashMap].
    *
    * Note this will perform a shallow conversion. If you want a deep conversion
    * you should use [toObservable].
    */
   factory ObservableMap.from(Map<K, V> other) {
-    var result = new ObservableMap<K, V>._createFromType(other);
-    other.forEach((key, value) { result[key] = value; });
-    return result;
+    return new ObservableMap<K, V>._createFromType(other)..addAll(other);
   }
 
   factory ObservableMap._createFromType(Map<K, V> other) {
     ObservableMap result;
     if (other is SplayTreeMap) {
       result = new ObservableMap<K, V>.sorted();
     } else if (other is LinkedHashMap) {
       result = new ObservableMap<K, V>.linked();
     } else {
       result = new ObservableMap<K, V>();
@@ skipping 24 matching lines @@
     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));
       }
     }
   }
 
+  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(key, isInsert: true));
     }
     return result;
   }
 
@@ skipping 15 matching lines @@
       });
       notifyPropertyChange(_LENGTH, len, 0);
     }
     _map.clear();
   }
 
   void forEach(void f(K key, V value)) => _map.forEach(f);
 
   String toString() => Maps.mapToString(this);
 }