Change "typedef" to "class" in core library and related tests.

tests/language/mixin_type_parameters_super_test.dart

Index: tests/language/mixin_type_parameters_super_test.dart
diff --git a/tests/language/mixin_type_parameters_super_test.dart b/tests/language/mixin_type_parameters_super_test.dart
index 020221981d5294fe8fb3d73ad95c46a0db76c2d1..eec1b625ed86f18fa1d4c91c1ff188b1b095ec18 100644
--- a/tests/language/mixin_type_parameters_super_test.dart
+++ b/tests/language/mixin_type_parameters_super_test.dart
@@ -40,10 +40,10 @@ class S<T> {
 class M {
 }
 
-typedef C0<T> = S with M;
-typedef C1<T> = S<T> with M;
-typedef C2<T> = S<int> with M;
-typedef C3 = S<String> with M;
+class C0<T> = S with M;
+class C1<T> = S<T> with M;
+class C2<T> = S<int> with M;
+class C3 = S<String> with M;
 
 main() {
   var c0 = new C0();