Fix issue #27830: the type of an super-set assignment expression is the type of

pkg/compiler/lib/src/inferrer/simple_types_inferrer.dart

Index: pkg/compiler/lib/src/inferrer/simple_types_inferrer.dart
diff --git a/pkg/compiler/lib/src/inferrer/simple_types_inferrer.dart b/pkg/compiler/lib/src/inferrer/simple_types_inferrer.dart
index 3507e5fab3d127fb2dc007ba59d77d26c358cbd0..f6cdaceffac2cc245792f6c055f5d8873bc9e034 100644
--- a/pkg/compiler/lib/src/inferrer/simple_types_inferrer.dart
+++ b/pkg/compiler/lib/src/inferrer/simple_types_inferrer.dart
@@ -1473,8 +1473,9 @@ class SimpleTypeInferrerVisitor<T>
     isThisExposed = true;
     Selector selector = elements.getSelector(node);
     TypeMask mask = inTreeData.typeOfSend(node);
-    return handleStaticSend(
+    handleStaticSend(
         node, selector, mask, element, new ArgumentsTypes<T>([rhsType], null));
+    return rhsType;
   }
 
   @override