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

tests/language/mixin_type_parameter2_test.dart

Index: tests/language/mixin_type_parameter2_test.dart
diff --git a/tests/language/mixin_type_parameter2_test.dart b/tests/language/mixin_type_parameter2_test.dart
index 27fe24546d073ab8184f7fe8370ec24a3bff7fbe..480777ebb28e4b61621695af605ee1f4792eac0f 100644
--- a/tests/language/mixin_type_parameter2_test.dart
+++ b/tests/language/mixin_type_parameter2_test.dart
@@ -14,7 +14,7 @@ class A {
   A(foo);
 }
 
-typedef MyTypedef<K, V> = A with Mixin1<K>, Mixin2<V>;
+class MyTypedef<K, V> = A with Mixin1<K>, Mixin2<V>;
 
 class B<K, V> extends MyTypedef<K, V> {
   B(foo) : super(foo);