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

tests/language/mixin_illegal_syntax_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.
 
 class S { }
 class G<T> { }
 class M { }
 
 typedef T0 = abstract S with M;
 abstract class T0A = S with M;
-typedef T1 = final S with M;     /// 01: compile-time error
-typedef T2 = var S with M;       /// 02: compile-time error
-typedef T3 = const S with M;     /// 03: compile-time error
-typedef T4 = static S with M;    /// 04: compile-time error
-typedef T5 = external S with M;  /// 05: compile-time error
-typedef T6 = G<int> with M;
-typedef T7 = G<Map<String,int>> with M;
+class T1 = final S with M;     /// 01: compile-time error
+class T2 = var S with M;       /// 02: compile-time error
+class T3 = const S with M;     /// 03: compile-time error
+class T4 = static S with M;    /// 04: compile-time error
+class T5 = external S with M;  /// 05: compile-time error
+class T6 = G<int> with M;
+class T7 = G<Map<String,int>> with M;
 
 class C0 extends abstract S with M { }  /// 06: compile-time error
 class C1 extends final S with M { }     /// 07: compile-time error
 class C2 extends var S with M { }       /// 08: compile-time error
 class C3 extends const S with M { }     /// 09: compile-time error
 class C4 extends static S with M { }    /// 10: compile-time error
 class C5 extends external S with M { }  /// 11: compile-time error
 class C6 extends G<int> with M { }
 class C7 extends G<Map<String,int>> with M { }
 
@@ skipping 19 matching lines @@
   new C2();  /// 08: continued
   new C3();  /// 09: continued
   new C4();  /// 10: continued
   new C5();  /// 11: continued
   new C6();
   new C7();
 
   new D0();  /// 12: continued
   new D1();
 }