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

tests/language/mixin_illegal_cycles_test.dart

Index: tests/language/mixin_illegal_cycles_test.dart
diff --git a/tests/language/mixin_illegal_cycles_test.dart b/tests/language/mixin_illegal_cycles_test.dart
index 472581f8366d358c660925888859ab6d91eaf549..9337fddf8d5eafab6a0cccd6ade3de914b195be4 100644
--- a/tests/language/mixin_illegal_cycles_test.dart
+++ b/tests/language/mixin_illegal_cycles_test.dart
@@ -4,21 +4,21 @@
 
 class M { }
 class M0 extends Object with M0 { }  /// 01: compile-time error
-typedef M1 = Object with M1;         /// 02: compile-time error
+class M1 = Object with M1;         /// 02: compile-time error
 
-typedef M2 = Object with M3;         /// 03: compile-time error
-typedef M3 = Object with M2;         /// 03: continued
+class M2 = Object with M3;         /// 03: compile-time error
+class M3 = Object with M2;         /// 03: continued
 
-typedef M4 = Object with M5;         /// 04: compile-time error
-typedef M5 = Object with M6;         /// 04: continued
-typedef M6 = Object with M4;         /// 04: continued
+class M4 = Object with M5;         /// 04: compile-time error
+class M5 = Object with M6;         /// 04: continued
+class M6 = Object with M4;         /// 04: continued
 
 class M7 extends Object with M8 { }  /// 05: compile-time error
 class M8 extends Object with M7 { }  /// 05: continued
 
-typedef M9  = Object with M91;       /// 06: compile-time error
-typedef M91 = Object with M92;       /// 06: continued
-typedef M92 = Object with M91;       /// 06: continued
+class M9  = Object with M91;       /// 06: compile-time error
+class M91 = Object with M92;       /// 06: continued
+class M92 = Object with M91;       /// 06: continued
 
 main() {
   new M0();  /// 01: continued