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

tests/language/mixin_mixin4_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import "package:expect/expect.dart";
 
 class I<T> { }
 
 class J<T> { }
 
 class S<T> { }
 
 class M<T> {
   t() { return T; }
 }
 
-typedef A<U, V> = Object with M<Map<U, V>> implements I<V>;
+class A<U, V> = Object with M<Map<U, V>> implements I<V>;
 
-typedef C<T, K> = S<T> with A<T, List<K>> implements J<K>;
+class C<T, K> = S<T> with A<T, List<K>> implements J<K>;
 
 main() {
   var c = new C<int, bool>();
   Expect.equals("Map<int, List<bool>>", c.t().toString());
   Expect.isTrue(c is I<List<bool>>);
   Expect.isTrue(c is J<bool>);
   Expect.isTrue(c is S<int>);
   Expect.isTrue(c is A<int, List<bool>>);
   Expect.isTrue(c is M<Map<int, List<bool>>>);
 }