See ActionGroup.fillContextMenu(IMenuManager menu) - you have to implement
this method in your ActionProvider to add corresponding action to the popup
menu.
/**
* Adds the applicable actions to a context menu,
* based on the state of the <code>ActionContext</code>.
* <p>
* The default implementation does nothing.
* Subclasses may override or extend this method.
* </p>
*
* @param menu the context menu manager
*/
public void fillContextMenu(IMenuManager menu) {
// do nothing
}