Dynamicize some mixin type tests

tests/language/mixin_mixin7_test.dart

 // Copyright (c) 2013, 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.
 
 import "package:expect/expect.dart";
 
 class I<T> { }
 
 class J<T> { }
 
 class K<T> { }
 
 class S<T> { }
 
 class M<T> {
   m() { return T; }
 }
 
 class A<U, V> = Object with M implements I<V>;  // M is raw.
 
 class B<T> = Object with A implements J<T>;  // A is raw.
 
 class C<T> = S<List<T>> with B implements K<T>;  // B is raw.
 
+@NoInline() @AssumeDynamic()
+dyn(x) => x;
+
 main() {
   var c = new C<int>();
   Expect.equals("dynamic", c.m().toString());
   Expect.isTrue(c is K<int>);
   Expect.isTrue(c is J);
   Expect.isTrue(c is I);
   Expect.isTrue(c is S<List<int>>);
   Expect.isTrue(c is A);
   Expect.isTrue(c is M);
+
+  Expect.equals("dynamic", dyn(c).m().toString());
+  Expect.isTrue(dyn(c) is K<int>);
+  Expect.isTrue(dyn(c) is J);
+  Expect.isTrue(dyn(c) is I);
+  Expect.isTrue(dyn(c) is S<List<int>>);
+  Expect.isTrue(dyn(c) is A);
+  Expect.isTrue(dyn(c) is M);
+
 }