Dynamicize some mixin type tests

tests/language/mixin_regress_13688_test.dart

Index: tests/language/mixin_regress_13688_test.dart
diff --git a/tests/language/mixin_regress_13688_test.dart b/tests/language/mixin_regress_13688_test.dart
index 00115394e45d789a6a68ddf8add312fd13682f42..d003741cdf10955e07a12bba90d42bc5559be762 100644
--- a/tests/language/mixin_regress_13688_test.dart
+++ b/tests/language/mixin_regress_13688_test.dart
@@ -12,7 +12,11 @@ class ComparableMixin<E> {
 
 class KUID extends Object with ComparableMixin<KUID> { }
 
+@NoInline() @AssumeDynamic()
+dyn(x) => x;
+
 main() {
   var kuid = new KUID();
   Expect.equals(kuid.runtimeType.toString(), kuid.e().toString());
+  Expect.equals(dyn(kuid).runtimeType.toString(), dyn(kuid).e().toString());
 }