Optimize needNoSuchMethodHandling computation

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

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library dart2js.world.class_set;
 
 import 'dart:collection' show IterableBase;
 
 import '../elements/elements.dart' show ClassElement;
 import '../util/enumset.dart' show EnumSet;
@@ skipping 443 matching lines @@
     if (_subtypes != null) {
       for (ClassHierarchyNode subtypeNode in _subtypes) {
         if (subtypeNode.isInstantiated) {
           return false;
         }
       }
     }
     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
   /// their corresponding [Instantiation] values in [mask]. If [strict] is
   /// `true`, [cls] itself is _not_ returned.
   Iterable<ClassElement> subclassesByMask(EnumSet<Instantiation> mask,
       {bool strict: false}) {
     return node.subclassesByMask(mask, strict: strict);
   }
 
@@ skipping 376 matching lines @@
   STOP,
 
   /// Iteration skips the subclasses of the current class.
   SKIP_SUBCLASSES,
 }
 
 /// Visiting function used for the `forEachX` functions of [ClassHierarchyNode]
 /// and [ClassSet]. The return value controls the continued iteration. If `null`
 /// is returned, iteration continues to the end.
 typedef IterationStep ForEachFunction(ClassElement cls);