Add test for initialization of the native interceptor dispatch property.

tests/html/js_dispatch_property_test_lib.dart

Index: tests/html/js_dispatch_property_test_lib.dart
diff --git a/tests/html/js_type_test_lib.dart b/tests/html/js_dispatch_property_test_lib.dart
similarity index 68%
copy from tests/html/js_type_test_lib.dart
copy to tests/html/js_dispatch_property_test_lib.dart
index 6b7113c42edbdc4097826c854eab5e3db9222494..77e371cf389debdb006e2568d6676d2a68fad97b 100644
--- a/tests/html/js_type_test_lib.dart
+++ b/tests/html/js_dispatch_property_test_lib.dart
@@ -3,11 +3,14 @@
 // BSD-style license that can be found in the LICENSE file.
 
 @JS()
-library js_type_test_lib;
+library js_dispatch_property_test_lib;
 
 import 'package:js/js.dart';
 
 @JS()
-class Foo {
-  external factory Foo();
+external A create();
+
+@JS() @anonymous
+class A {
+  external String foo(String x);
 }