Instead of applying a transform for every RenderObject, pass down an Offset for where to paint.

sky/sdk/lib/rendering/stack.dart

Index: sky/sdk/lib/rendering/stack.dart
diff --git a/sky/sdk/lib/rendering/stack.dart b/sky/sdk/lib/rendering/stack.dart
index 747ffdf8f75fd1189399aa6ec48e6561b2ad1c28..d96311226e481168440992fbcfd62a98c41d71f7 100644
--- a/sky/sdk/lib/rendering/stack.dart
+++ b/sky/sdk/lib/rendering/stack.dart
@@ -195,7 +195,7 @@ class RenderStack extends RenderBox with ContainerRenderObjectMixin<RenderBox, S
     defaultHitTestChildren(result, position: position);
   }
 
-  void paint(RenderCanvas canvas) {
-    defaultPaint(canvas);
+  void paint(RenderCanvas canvas, Offset offset) {
+    defaultPaint(canvas, offset);
   }
 }