add staggered test.

samples/ControlCatalog/Pages/ItemsRepeaterPage.xaml

@@ -12,8 +12,9 @@
         <ComboBoxItem>Stack - Horizontal</ComboBoxItem>
         <ComboBoxItem>UniformGrid - Vertical</ComboBoxItem>
         <ComboBoxItem>UniformGrid - Horizontal</ComboBoxItem>
-        <ComboBoxItem>WrapLayout - Horizontal</ComboBoxItem>
-        <ComboBoxItem>WrapLayout - Veritcal</ComboBoxItem>
+        <ComboBoxItem>Wrap - Horizontal</ComboBoxItem>
+        <ComboBoxItem>Wrap - Veritcal</ComboBoxItem>
+        <ComboBoxItem>Staggered - Horizontal</ComboBoxItem>
       </ComboBox>
       <Button Command="{Binding AddItem}">Add Item</Button>
       <Button Command="{Binding RandomizeHeights}">Randomize Heights</Button>

samples/ControlCatalog/Pages/ItemsRepeaterPage.xaml.cs

@@ -90,6 +90,16 @@ namespace ControlCatalog.Pages
                         VerticalSpacing = 20
                     };
                     break;
+                case 6:
+                    _scroller.HorizontalScrollBarVisibility = ScrollBarVisibility.Disabled;
+                    _scroller.VerticalScrollBarVisibility = ScrollBarVisibility.Auto;
+                    _repeater.Layout = new StaggeredLayout
+                    {
+                         ColumnSpacing = 20,
+                          RowSpacing = 20,
+                          DesiredColumnWidth= 250
+                    };
+                    break;
             }
         }