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

tests/language/mixin_implements_test.dart

Index: tests/language/mixin_implements_test.dart
diff --git a/tests/language/mixin_implements_test.dart b/tests/language/mixin_implements_test.dart
index 3eaad79400bd16be968723f2e61bb401433cfe8b..0136eb735e1183f261c5eaa008fcf12e15347e0c 100644
--- a/tests/language/mixin_implements_test.dart
+++ b/tests/language/mixin_implements_test.dart
@@ -20,12 +20,12 @@ class M {
   bar() => 87;
 }
 
-typedef C0 = Object with M;
-typedef C1 = Object with M implements I0;
-typedef C2 = Object with M implements I1;
-typedef C3 = Object with M implements I0, I1;
-typedef C4 = Object with M implements I1, I0;
-typedef C5 = Object with M implements I2;
+class C0 = Object with M;
+class C1 = Object with M implements I0;
+class C2 = Object with M implements I1;
+class C3 = Object with M implements I0, I1;
+class C4 = Object with M implements I1, I0;
+class C5 = Object with M implements I2;
 
 main() {
   var c0 = new C0();