Remove ClassWorld.subclassesOf and ClassWorld.subtypesOf.

pkg/compiler/lib/src/inferrer/concrete_types_inferrer.dart

Index: pkg/compiler/lib/src/inferrer/concrete_types_inferrer.dart
diff --git a/pkg/compiler/lib/src/inferrer/concrete_types_inferrer.dart b/pkg/compiler/lib/src/inferrer/concrete_types_inferrer.dart
index 9369d1def75adfd38a67745050625a8b004259d1..19bcab436d6674d8de30bb2727a18517fec797c8 100644
--- a/pkg/compiler/lib/src/inferrer/concrete_types_inferrer.dart
+++ b/pkg/compiler/lib/src/inferrer/concrete_types_inferrer.dart
@@ -557,12 +557,12 @@ class ConcreteTypeSystem extends TypeSystem<ConcreteType> {
 
   @override
   ConcreteType nonNullSubclass(ClassElement cls) {
-    return nonNullSubX(cls, compiler.world.subclassesOf);
+    return nonNullSubX(cls, compiler.world.strictSubclassesOf);
   }
 
   @override
   ConcreteType nonNullSubtype(ClassElement cls) {
-    return nonNullSubX(cls, compiler.world.subtypesOf);
+    return nonNullSubX(cls, compiler.world.strictSubtypesOf);
   }
 
   @override