Create VarianceChecker

core/descriptors/src/org/jetbrains/jet/lang/descriptors/Visibilities.java

@@ -57,6 +57,8 @@ public class Visibilities {
         }
     };
 
+    public static final Visibility PRIVATE_TO_THIS = PRIVATE;
+
     public static final Visibility PROTECTED = new Visibility("protected", true) {
         @Override
         protected boolean isVisible(@NotNull DeclarationDescriptorWithVisibility what, @NotNull DeclarationDescriptor from) {
@@ -174,4 +176,8 @@ public class Visibilities {
         }
         return null;
     }
+
+    public static boolean isPrivate(@NotNull Visibility visibility) {
+        return visibility == PRIVATE || visibility == PRIVATE_TO_THIS;
+    }
 }