Revert "Parts must start with 'part of'" and "Attempt to fix VM build"

dart/samples/ui_lib/observable/ChangeEvent.dart

-part of observable;
-
 // Copyright (c) 2011, 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.
 
 /** A change to an observable instance. */
 class ChangeEvent {
   // TODO(sigmund): capture language issues around enums & create a cannonical
   // Dart enum design.
   /** Type denoting an in-place update event. */
   static const UPDATE = 0;
@@ skipping 66 matching lines @@
         for (final listener in obj.listeners) {
           listener(this);
         }
       }
     }
   }
 }
 
 /** A listener of change events. */
 typedef void ChangeListener(EventSummary events);