Change "typedef" to "class" in core library and related tests.

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;
 
 /**
  * Interface representing an observable object. This is used by data in
  * model-view architectures to notify interested parties of [changes].
  *
@@ skipping 59 matching lines @@
    */
   static void dirtyCheck() => dirtyCheckObservables();
 }
 
 /**
  * Base class implementing [Observable].
  *
  * When a field, property, or indexable item is changed, the change record
  * will be sent to [changes].
  */
-typedef ObservableBase = Object with ObservableMixin;
+class ObservableBase = Object with ObservableMixin;
 
 /**
  * Mixin for implementing [Observable] objects.
  *
  * When a field, property, or indexable item is changed, the change record
  * will be sent to [changes].
  */
 abstract class ObservableMixin implements Observable {
   StreamController _changes;
   InstanceMirror _mirror;
@@ skipping 114 matching lines @@
 _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;
 }