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

tests/language/mixin_type_parameter4_test.dart

Index: tests/language/mixin_type_parameter4_test.dart
diff --git a/tests/language/mixin_type_parameter4_test.dart b/tests/language/mixin_type_parameter4_test.dart
index 00fe43e3e55fa8fba613473dea8a6a1fd966af26..8f35d8f110db729ab4a366baf23c8acf4e0ff87f 100644
--- a/tests/language/mixin_type_parameter4_test.dart
+++ b/tests/language/mixin_type_parameter4_test.dart
@@ -13,7 +13,7 @@ class B2 {}
 
 class A1<T> extends B1 with M<T> {}
 
-typedef A2<T> = B2 with M<T>;
+class A2<T> = B2 with M<T>;
 
 main() {
   var ab = new A1<int>();