Fix casts and type assertions on mixins used in native classes

sdk/lib/_internal/compiler/implementation/compiler.dart

Index: sdk/lib/_internal/compiler/implementation/compiler.dart
diff --git a/sdk/lib/_internal/compiler/implementation/compiler.dart b/sdk/lib/_internal/compiler/implementation/compiler.dart
index fe2403ed7a601170c0b653b04cdb18b1d5eb119b..4b172e987a002dcea50178d0319e21db82ea5f8b 100644
--- a/sdk/lib/_internal/compiler/implementation/compiler.dart
+++ b/sdk/lib/_internal/compiler/implementation/compiler.dart
@@ -164,7 +164,9 @@ abstract class Backend {
                        TreeElements elements) {}
 
   /// Register an as check to the backend.
-  void registerAsCheck(DartType type, TreeElements elements) {}
+  void registerAsCheck(DartType type,
+                       Enqueuer enqueuer,
+                       TreeElements elements) {}
 
   /// Register that the application may throw a [NoSuchMethodError].
   void registerThrowNoSuchMethod(TreeElements elements) {}