Fix function subtyping crash

test/codegen/language/function_subtype_regression_ddc_588_test.dart

Index: test/codegen/language/function_subtype_regression_ddc_588_test.dart
diff --git a/test/codegen/language/function_subtype_regression_ddc_588_test.dart b/test/codegen/language/function_subtype_regression_ddc_588_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..ece2757b97e145d717342e312cef9eaf89ee7256
--- /dev/null
+++ b/test/codegen/language/function_subtype_regression_ddc_588_test.dart
@@ -0,0 +1,14 @@
+import "package:expect/expect.dart";
+
+// regression test for ddc #588
+
+typedef int Int2Int(int x);
+
+void foo(List<Int2Int> list) {
+  list.forEach((f) => print(f(42)));
+}
+
+void main() {
+  var l = <Function>[];
+  Expect.throws(() => foo(l), (e) => e is TypeError);
+}