/// <summary>
        /// Raises the OnHistory change.
        /// </summary>
        protected void RaiseOnHistoryChange(HistoryChangeEventArgs e)
        {
            EventHandler <HistoryChangeEventArgs> handler = OnHistoryChange;

            if (handler != null)
            {
                handler(this, e);
            }
        }
 // ------------------------------------------------------------------
 /// <summary>
 /// Bubbles the OnHistoryChange event from the Controller to the surface
 /// </summary>
 /// <param name="sender">The source of the event.</param>
 /// <param name="e">The
 /// <see cref="T:Netron.Diagramming.Core.HistoryChangeEventArgs"/>
 /// instance containing the event data.</param>
 // ------------------------------------------------------------------
 void mController_OnHistoryChange(
     object sender,
     HistoryChangeEventArgs e)
 {
     RaiseOnHistoryChange(e);
 }