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

tests/language/mixin_mixin7_test.dart

Index: tests/language/mixin_mixin7_test.dart
diff --git a/tests/language/mixin_mixin7_test.dart b/tests/language/mixin_mixin7_test.dart
index 2e56355c14fc422efb00428fa55db025f613e30e..9bbb4932001983419eced5ccbd998a8166c3a748 100644
--- a/tests/language/mixin_mixin7_test.dart
+++ b/tests/language/mixin_mixin7_test.dart
@@ -16,11 +16,11 @@ class M<T> {
   m() { return T; }
 }
 
-typedef A<U, V> = Object with M implements I<V>;  // M is raw.
+class A<U, V> = Object with M implements I<V>;  // M is raw.
 
-typedef B<T> = Object with A implements J<T>;  // A is raw.
+class B<T> = Object with A implements J<T>;  // A is raw.
 
-typedef C<T> = S<List<T>> with B implements K<T>;  // B is raw.
+class C<T> = S<List<T>> with B implements K<T>;  // B is raw.
 
 main() {
   var c = new C<int>();