Add test for crash with js-interop @anonymous feature

tests/compiler/dart2js_extra/interop_anonymous_unreachable_test.dart

Index: tests/compiler/dart2js_extra/interop_anonymous_unreachable_test.dart
diff --git a/tests/compiler/dart2js_extra/interop_anonymous_unreachable_test.dart b/tests/compiler/dart2js_extra/interop_anonymous_unreachable_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..b734491e654758c1b47b36687133d78bbfb75e97
--- /dev/null
+++ b/tests/compiler/dart2js_extra/interop_anonymous_unreachable_test.dart
@@ -0,0 +1,14 @@
+// Copyright (c) 2015, Google Inc. 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.
+
+import 'package:js/js.dart';
+
+@JS()
+@anonymous
+class A {
+  external bool get value;
+  external factory A({bool value});

[Siggi Cherem (dart-lang), 2015/11/18 23:44:58]

technically you don't even need this argument/field, but I'm keeping it because
otherwise there is no need to have an @anonymous object.

+}
+
+void main() {}