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

tests/language/mixin_illegal_static_access_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 S {
   static foo() => 42;
 }
 
 class M {
   static bar() => 87;
 }
 
-typedef C = S with M;
+class C = S with M;
 
 main() {
   Expect.equals(42, S.foo());
   Expect.equals(87, M.bar());
 
   Expect.throws(() => C.foo(), (e) => e is NoSuchMethodError);
   Expect.throws(() => C.bar(), (e) => e is NoSuchMethodError);
 }