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

tests/language/mixin_mixin3_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 M<T> {
   t() { return T; }
 }
 
-typedef A<U> = Object with M<List<U>>;
+class A<U> = Object with M<List<U>>;
 
-typedef B0 = Object with A<Set<bool>>;
+class B0 = Object with A<Set<bool>>;
 
-typedef B1 = Object with A<Set<int>>;
+class B1 = Object with A<Set<int>>;
 
 class C0 extends B0 { }
 
 class C1 extends B1 { }
 
-typedef A2<K, V> = Object with M<Map<K, V>>;
+class A2<K, V> = Object with M<Map<K, V>>;
 
-typedef B2<V> = Object with A2<Set<V>, List<V>>;
+class B2<V> = Object with A2<Set<V>, List<V>>;
 
-typedef B3<K, V> = Object with A2<Set<K>, List<V>>;
+class B3<K, V> = Object with A2<Set<K>, List<V>>;
 
 class C2<T> extends B2<T> { }
 
 class C3<T> extends B3<T, int> { }
 
 class N {
   q() { return 42; }
 }
 
-typedef O<U> = Object with N;
+class O<U> = Object with N;
 
-typedef P<K, V> = Object with O<V>;
+class P<K, V> = Object with O<V>;
 
 class Q<K, V> extends P<K, V> { }
 
 main() {
   Expect.equals("List<Set<bool>>", new C0().t().toString());
   Expect.equals("List<Set<int>>", new C1().t().toString());
   Expect.equals("Map<Set<bool>, List<bool>>", new C2<bool>().t().toString());
   Expect.equals("Map<Set<bool>, List<int>>", new C3<bool>().t().toString());
   Expect.equals(42, new Q<bool, int>().q());
 }