fix more mixin tests to work in strong mode

tests/language_strong/mixin_super_bound_test.dart

Index: tests/language_strong/mixin_super_bound_test.dart
diff --git a/tests/language_strong/mixin_super_bound_test.dart b/tests/language_strong/mixin_super_bound_test.dart
index fe6a283b4b5a97516cbb59065a466f85b65b80f3..4c3d910e70bf3d8b323490e20cd8243c8a73d706 100644
--- a/tests/language_strong/mixin_super_bound_test.dart
+++ b/tests/language_strong/mixin_super_bound_test.dart
@@ -6,8 +6,7 @@ import "package:expect/expect.dart";
 
 bool inCheckedMode() {
   try {
-    var i = 42;
-    String s = i;
+    String s = 42 as dynamic;
   } on TypeError catch (e) {
     return true;
   }
@@ -20,9 +19,10 @@ class N<U, V extends U> {}
 
 class S<T> {}
 
-class MNA<U, V, W> extends S<List<U>> with M<V, U>, N<List<W>, List<W>> {}
+class MNA<U, V extends U, W> extends S<List<U>>
+    with M<V, U>, N<List<W>, List<W>> {}
 
-class MNA2<U, V, W> = S<List<U>> with M<V, U>, N<List<W>, List<W>>;
+class MNA2<U, V extends U, W> = S<List<U>> with M<V, U>, N<List<W>, List<W>>;
 
 main() {
   new MNA<num, int, bool>();