Move observe to observe 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 174 matching lines @@
    * will not schedule [deliverChanges]; use [Observable.dirtyCheck] instead.
    */
   void notifyChange(ChangeRecord record) {
     if (!hasObservers) return;
 
     if (_records == null) _records = [];
     _records.add(record);
   }
 }
 
+/**
+ * Notify the property change. Shorthand for:
+ *
+ *     target.notifyChange(new PropertyChangeRecord(targetName));
+ */
+void notifyProperty(Observable target, Symbol targetName) {
+  target.notifyChange(new PropertyChangeRecord(targetName));
+}
+
 // TODO(jmesserly): remove the instance method and make this top-level method
 // public instead?
 _notifyPropertyChange(Observable obj, Symbol field, Object oldValue,
     Object newValue) {
 
   // TODO(jmesserly): should this be == instead of identical, to prevent
   // spurious loops?
   if (obj.hasObservers && !identical(oldValue, newValue)) {
     obj.notifyChange(new PropertyChangeRecord(field));
   }
   return newValue;
 }
 
 
 /**
  * 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();
 }