Add test for initialization of the native interceptor dispatch property.

tests/html/js_dispatch_property_test_js.js

Index: tests/html/js_dispatch_property_test_js.js
diff --git a/tests/html/js_dispatch_property_test_js.js b/tests/html/js_dispatch_property_test_js.js
new file mode 100644
index 0000000000000000000000000000000000000000..8f10dcc8ec9f0f3394b0dd8b11e976ffdbd4b8a5
--- /dev/null
+++ b/tests/html/js_dispatch_property_test_js.js
@@ -0,0 +1,17 @@
+// Copyright (c) 2016, 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.
+
+self.create = function() {
+  return {
+    // If the dispatch property name is uninitialized, it will be `undefined` or
+    // `null`, which will match these properties on dispatch record
+    // lookup. These properties map to malformed dispatch records to force an
+    // error.
+
+    'undefined': {p: false},
+    'null': {p: false},
+
+    foo: function(x) { return 'Foo ' + x; },
+  };
+}