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

tests/language/mixin_illegal_super_use_test.dart

Index: tests/language/mixin_illegal_super_use_test.dart
diff --git a/tests/language/mixin_illegal_super_use_test.dart b/tests/language/mixin_illegal_super_use_test.dart
index 7f12e4d6f1b87b45fc57440816084068cf303a5c..7f0d64a39de0173b8d9520ae6c9decd24064d1d4 100644
--- a/tests/language/mixin_illegal_super_use_test.dart
+++ b/tests/language/mixin_illegal_super_use_test.dart
@@ -57,10 +57,10 @@ class P2 {
   }
 }
 
-typedef C = Object with M;
-typedef D = Object with P0;
-typedef E = Object with M, P1;
-typedef F = Object with P2, M;
+class C = Object with M;
+class D = Object with P0;
+class E = Object with M, P1;
+class F = Object with P2, M;
 
 main() {
   var p1 = new P1();