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

tests/language/mixin_illegal_syntax_test.dart

Index: tests/language/mixin_illegal_syntax_test.dart
diff --git a/tests/language/mixin_illegal_syntax_test.dart b/tests/language/mixin_illegal_syntax_test.dart
index 6d0177d5fce02def9c1682722c8371b522580fb7..c7b3753f155f64506ff7804d5c997578416c9e89 100644
--- a/tests/language/mixin_illegal_syntax_test.dart
+++ b/tests/language/mixin_illegal_syntax_test.dart
@@ -8,13 +8,13 @@ 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