add custom_element package

pkg/observe/lib/src/observable.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;
 
 /**
  * Use `@observable` to make a field automatically observable.
  */
 const Object observable = const _ObservableAnnotation();
@@ skipping 45 matching lines @@
   /**
    * Notify observers of a change.
    *
    * For most objects [ObservableMixin.notifyPropertyChange] is more
    * convenient, but collections sometimes deliver other types of changes such
    * as a [ListChangeRecord].
    */
   void notifyChange(ChangeRecord record);
 
   /**
+   * True if this object has any observers, and should call
+   * [notifyChange] for changes.
+   */
+  bool get hasObservers;
+
+  /**
    * Performs dirty checking of objects that inherit from [ObservableMixin].
    * This scans all observed objects using mirrors and determines if any fields
    * have changed. If they have, it delivers the changes for the object.
    */
   static void dirtyCheck() => dirtyCheckObservables();
 }
 
 /**
  * Base class implementing [Observable].
  *
@@ skipping 16 matching lines @@
   List<ChangeRecord> _records;
 
   Stream<List<ChangeRecord>> get changes {
     if (_changes == null) {
       _changes = new StreamController.broadcast(sync: true,
           onListen: _observed, onCancel: _unobserved);
     }
     return _changes.stream;
   }
 
-  /**
-   * True if this object has any observers, and should call
-   * [notifyPropertyChange] for changes.
-   */
   bool get hasObservers => _changes != null && _changes.hasListener;
 
   void _observed() {
     // Register this object for dirty checking purposes.
     registerObservable(this);
 
     var mirror = reflect(this);
     var values = new Map<Symbol, Object>();
 
     // TODO(jmesserly): this should consider the superclass. Unfortunately
@@ skipping 91 matching lines @@
 /**
  * The type of the `@observable` annotation.
  *
  * Library private because you should be able to use the [observable] field
  * to get the one and only instance. We could make it public though, if anyone
  * needs it for some reason.
  */
 class _ObservableAnnotation {
   const _ObservableAnnotation();
 }