Fix crash when deferred loading would encounter an unresolved super setter.

tests/language/deferred_super_dependency_lib.dart

Index: tests/language/deferred_super_dependency_lib.dart
diff --git a/tests/language/deferred_type_dependency_lib3.dart b/tests/language/deferred_super_dependency_lib.dart
similarity index 80%
copy from tests/language/deferred_type_dependency_lib3.dart
copy to tests/language/deferred_super_dependency_lib.dart
index 9a23fc960f3a41a78bc94be3ec5b94d01b130256..a592dabbae9fbb321b2f5c088e1267997af0e6fa 100644
--- a/tests/language/deferred_type_dependency_lib3.dart
+++ b/tests/language/deferred_super_dependency_lib.dart
@@ -2,9 +2,11 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-library lib3;
-
 class A {
-  var p = true;
 }
 
+class C extends A {
+  foo() {
+    super.foo = 3;
+  }
+}