add icons

Samples/UIWidgetsSamples_2019_4/Assets/UIWidgetsGallery/demo/shrine/backdrop.cs

                         icon: new Stack(children: new List<Widget>{
                             new Opacity(
                               opacity: animation.value,
-                              child:  new Container(
-                                  width: 44.0f,
-                                  height: 44.0f,
+                              child: new Container(
+                                  width: 20.0f,
+                                  height: 20.0f,
-                                              file: "logo.png"
+                                              file: "shrine_images/slanted_menu.png"
                                           )
                                       ),
                                       shape: BoxShape.circle
                               begin: Offset.zero,
                               end: new Offset(1.0f, 0.0f)).evaluate(animation),
                               child: new Container(
-                                  width: 44.0f,
-                                  height: 44.0f,
+                                  width: 20.0f,
+                                  height: 20.0f,
-                                              file: "logo.png"
+                                              file: "shrine_images/diamond.png"
                                           )
                                       ),
                                       shape: BoxShape.circle

Samples/UIWidgetsSamples_2019_4/Assets/UIWidgetsGallery/demo/shrine/shopping_cart.cs

 public class _ShoppingCartPageState : State<ShoppingCartPage> {
   List<Widget> _createShoppingCartRows(AppStateModel model)
   {
-    List<Widget> widgets = null;
+    List<Widget> widgets = new List<Widget>();
     for (int id = 0; id < model.productsInCart.Count; id++)
     {
       widgets.Add(new ShoppingCartRow(