Fix crash for type variables with dynamic bound.

tests/language/regress_19728_test.dart

 // Copyright (c) 2014, 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.
-library pop_pop_win.game_web;
 
-import 'platform_web.dart';
-import 'package:pop_pop_win/pop_pop_win.dart';
+// Regression test for issue 19728.
+
+class C<T extends dynamic> {
+  T field;
+
+  test() {
+    field = 0;
+    int i = field;
+  }
+}
 
 void main() {
-  startGame(new PlatformWeb());
-}
+  new C().test();
+}