title: Watching property changes on Dart polymer-element
body: <p>Is there a way to watch property changes on Dart polymer-element as described in <a href="http://www.polymer-project.org/polymer.html#change-watchers" rel="nofollow">Change watchers</a> section?  I tried adding <code>void myattributeChanged(String oldValue)</code> method but it does not get called.</p>