Optimize needNoSuchMethodHandling computation

pkg/compiler/lib/src/universe/class_set.dart

Index: pkg/compiler/lib/src/universe/class_set.dart
diff --git a/pkg/compiler/lib/src/universe/class_set.dart b/pkg/compiler/lib/src/universe/class_set.dart
index 2dd892ef431b5c258c62e579255556db2a4a07c4..637fd168f1c891cd59fa934c21897837dd8384d3 100644
--- a/pkg/compiler/lib/src/universe/class_set.dart
+++ b/pkg/compiler/lib/src/universe/class_set.dart
@@ -461,6 +461,10 @@ class ClassSet {
     return true;
   }
 
+  Iterable<ClassHierarchyNode> get subtypeNodes {
+    return _subtypes ?? const <ClassHierarchyNode>[];
+  }
+
   /// Returns an [Iterable] of the subclasses of [cls] possibly including [cls].
   ///
   /// Subclasses are included if their instantiation properties intersect with