Replace setBoxDecoration() with a decoration property.

sky/examples/raw/simple_render_tree.dart

Index: sky/examples/raw/simple_render_tree.dart
diff --git a/sky/examples/raw/simple_render_tree.dart b/sky/examples/raw/simple_render_tree.dart
index 7740970d99b1ecc821b7bb0be9f61ea726810f0d..552cf552d9553cacddc3e9629e35a5e5b882ce71 100644
--- a/sky/examples/raw/simple_render_tree.dart
+++ b/sky/examples/raw/simple_render_tree.dart
@@ -30,9 +30,9 @@ class RenderSolidColor extends RenderDecoratedBox {
 
   void handlePointer(PointerEvent event) {
     if (event.type == 'pointerdown')
-      setBoxDecoration(new BoxDecoration(backgroundColor: 0xFFFF0000));
+      decoration = new BoxDecoration(backgroundColor: 0xFFFF0000);
     else if (event.type == 'pointerup')
-      setBoxDecoration(new BoxDecoration(backgroundColor: backgroundColor));
+      decoration = new BoxDecoration(backgroundColor: backgroundColor);
   }
 }