Move observe to observe package

pkg/observe/lib/src/observable.dart

Index: pkg/observe/lib/src/observable.dart
diff --git a/pkg/observe/lib/src/observable.dart b/pkg/observe/lib/src/observable.dart
index 7610a0f21e176a7104f50783f28d20726b9201b7..0127d6e0c8525e91529db696d48a1de545d1ccad 100644
--- a/pkg/observe/lib/src/observable.dart
+++ b/pkg/observe/lib/src/observable.dart
@@ -192,6 +192,15 @@ abstract class ObservableMixin implements Observable {
   }
 }
 
+/**
+ * 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,