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

tests/language/mixin_mixin6_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 K<T> { }
 
 class S<T> { }
 
 class M<T> {
   m() { 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 B<T> = Object with A<T, Set<T>> implements J<T>;
+class B<T> = Object with A<T, Set<T>> implements J<T>;
 
-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>();
   Expect.equals("Map<dynamic, Set>", c.m().toString());
   Expect.isTrue(c is K<int>);
   Expect.isTrue(c is J);
   Expect.isTrue(c is I<Set>);
   Expect.isTrue(c is S<List<int>>);
   Expect.isTrue(c is A<dynamic, Set>);
   Expect.isTrue(c is M<Map<dynamic, Set>>);
 }