For improvement of docking performance, UpdateChildren is not done except DirectChildrenChanged

ExtendedWPFToolkitSolution/Src/Xceed.Wpf.AvalonDock/Controls/LayoutGridControl.cs

@@ -72,6 +72,8 @@ namespace Xceed.Wpf.AvalonDock.Controls
 
             _model.ChildrenTreeChanged += (s, args) =>
                 {
+                    if (args.Change != ChildrenTreeChange.DirectChildrenChanged)
+                        return;
                     if (_asyncRefreshCalled.HasValue &&
                         _asyncRefreshCalled.Value == args.Change)
                         return;