private void RemoveFromActiveList(IDockContent content)
{
if (this.LastActiveContent == content)
this.LastActiveContent = content.DockHandler.PreviousActive;
IDockContent prev = content.DockHandler.PreviousActive;
IDockContent next = content.DockHandler.NextActive;
if (prev != null)
prev.DockHandler.NextActive = next;
if (next != null)
next.DockHandler.PreviousActive = prev;
content.DockHandler.PreviousActive = null;
content.DockHandler.NextActive = null;
}