Make sure we can use JavaScript properties on Object as classes.

tests/language/js_properties_test.dart

+// Copyright (c) 2012, 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.
+// Test that JavaScript properties on Object can still be classes in
+// Dart.
+
+void main() {
+  Expect.equals(42, new __defineGetter__().hello());
+  Expect.equals(42, new __defineSetter__().hello());
+  Expect.equals(42, new __lookupGetter__().hello());
+  Expect.equals(42, new __lookupSetter__().hello());
+  Expect.equals(42, new constructor().hello());
+  Expect.equals(42, new hasOwnProperty().hello());
+  Expect.equals(42, new isPrototypeOf().hello());
+  Expect.equals(42, new propertyIsEnumerable().hello());
+  Expect.equals(42, new toLocaleString().hello());
+  Expect.equals(42, new toString().hello());
+  Expect.equals(42, new valueOf().hello());
+}
+
+class Hello {
+  int hello() => 42;
+}
+
+class __defineGetter__ extends Hello {}
+class __defineSetter__ extends Hello {}
+class __lookupGetter__ extends Hello {}
+class __lookupSetter__ extends Hello {}
+class constructor extends Hello {}
+class hasOwnProperty extends Hello {}
+class isPrototypeOf extends Hello {}
+class propertyIsEnumerable extends Hello {}
+class toLocaleString extends Hello {}
+class toString extends Hello {}
+class valueOf extends Hello {}