Add regression test for issue 34392.

Bug: https://github.com/dart-lang/sdk/issues/34392
Change-Id: Ia86264e8e752d7563b97657321f92eaa53f257bb
Reviewed-on: https://dart-review.googlesource.com/76180
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
diff --git a/tests/language_2/regress_34392_test.dart b/tests/language_2/regress_34392_test.dart
new file mode 100644
index 0000000..286d8e1
--- /dev/null
+++ b/tests/language_2/regress_34392_test.dart
@@ -0,0 +1,19 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// 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.
+
+abstract class I {
+  foo([a]);
+}
+
+abstract class A {
+  foo() {}
+}
+
+abstract class B extends A implements I {}
+
+class C extends B {
+  foo([a]) {}
+}
+
+void main() {}