Clean up some warnings.

editor/tools/plugins/com.google.dart.tools.core/src/com/google/dart/tools/core/model/ElementChangedEvent.java

Index: editor/tools/plugins/com.google.dart.tools.core/src/com/google/dart/tools/core/model/ElementChangedEvent.java
===================================================================
--- editor/tools/plugins/com.google.dart.tools.core/src/com/google/dart/tools/core/model/ElementChangedEvent.java	(revision 11395)
+++ editor/tools/plugins/com.google.dart.tools.core/src/com/google/dart/tools/core/model/ElementChangedEvent.java	(working copy)
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2011, the Dart project authors.
+ * Copyright (c) 2012, the Dart project authors.
  * 
  * Licensed under the Eclipse Public License v1.0 (the "License"); you may not use this file except
  * in compliance with the License. You may obtain a copy of the License at
@@ -21,6 +21,8 @@
  * delta object carried by this event.
  */
 public class ElementChangedEvent extends EventObject {
+  private static final long serialVersionUID = 1L;
+
   /**
    * Event type constant (bit mask) indicating an after-the-fact report of creations, deletions, and
    * modifications to one or more Dart element(s) expressed as a hierarchical Dart element delta as