Insert covariance checks in strong mode.

pkg/kernel/lib/target/vm.dart

Index: pkg/kernel/lib/target/vm.dart
diff --git a/pkg/kernel/lib/target/vm.dart b/pkg/kernel/lib/target/vm.dart
index 855857c071fa2352dd75f07a01892f2bce0a898b..58c229dc14f26bf444fa29fba003d5a5de3d2320 100644
--- a/pkg/kernel/lib/target/vm.dart
+++ b/pkg/kernel/lib/target/vm.dart
@@ -4,8 +4,10 @@
 library kernel.target.vm;
 
 import '../ast.dart';
+import '../core_types.dart';
 import '../transformations/continuation.dart' as cont;
 import '../transformations/erasure.dart';
+import '../transformations/insert_covariance_checks.dart';
 import '../transformations/insert_type_checks.dart';
 import '../transformations/mixin_full_resolution.dart' as mix;
 import '../transformations/sanitize_for_vm.dart';
@@ -52,10 +54,16 @@ class VmTarget extends Target {
       ];
 
   void transformProgram(Program program) {
-    new mix.MixinFullResolution().transform(program);
+    var mixins = new mix.MixinFullResolution();
+    mixins.transform(program);
 
     if (strongMode) {
-      new InsertTypeChecks().transformProgram(program);
+      var hierarchy = mixins.hierarchy;
+      var coreTypes = new CoreTypes(program);
+      new InsertTypeChecks(hierarchy: hierarchy, coreTypes: coreTypes)
+          .transformProgram(program);
+      new InsertCovarianceChecks(hierarchy: hierarchy, coreTypes: coreTypes)
+          .transformProgram(program);
     }
 
     cont.transformProgram(program);