Dynamicize some mixin type tests

tests/language/regress_18713_test.dart

Index: tests/language/regress_18713_test.dart
diff --git a/tests/language/regress_18713_test.dart b/tests/language/regress_18713_test.dart
index b0d87360f55db09a1be350712ddcc3d810397fc1..7e9f32bd29c1bad114ae00ae8b3e7da44e25daed 100644
--- a/tests/language/regress_18713_test.dart
+++ b/tests/language/regress_18713_test.dart
@@ -16,10 +16,19 @@ class S<Y> {
 
 class TS<A, B> = T<A> with S<B>;
 
+@NoInline() @AssumeDynamic()
+dyn(x) => x;
+
 main() {
   var ts = new TS<int, String>();
+
   Expect.equals("String", ts.sType.toString());
   Expect.equals("int", ts.tType.toString());
   Expect.equals("String", ts.getSType.toString());
   Expect.equals("int", ts.getTType.toString());
+
+  Expect.equals("String", dyn(ts).sType.toString());
+  Expect.equals("int", dyn(ts).tType.toString());
+  Expect.equals("String", dyn(ts).getSType.toString());
+  Expect.equals("int", dyn(ts).getTType.toString());
 }