dart2js cps: Use TypeMaskSystem when inserting refinement nodes.

pkg/compiler/lib/src/world.dart

 // Copyright (c) 2012, 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;
 
 import 'closure.dart' show
     SynthesizedCallMethodElementX;
 import 'common/backend_api.dart' show
     Backend;
@@ skipping 113 matching lines @@
 }
 
 class World implements ClassWorld {
   ClassElement get objectClass => compiler.objectClass;
   ClassElement get functionClass => compiler.functionClass;
   ClassElement get boolClass => compiler.boolClass;
   ClassElement get numClass => compiler.numClass;
   ClassElement get intClass => compiler.intClass;
   ClassElement get doubleClass => compiler.doubleClass;
   ClassElement get stringClass => compiler.stringClass;
+  ClassElement get nullClass => compiler.nullClass;
 
   /// Cache of [ti.FlatTypeMask]s grouped by the 8 possible values of the
   /// [ti.FlatTypeMask.flags] property.
   List<Map<ClassElement, ti.TypeMask>> canonicalizedTypeMasks =
       new List<Map<ClassElement, ti.TypeMask>>.filled(8, null);
 
   bool checkInvariants(ClassElement cls, {bool mustBeInstantiated: true}) {
     return
       invariant(cls, cls.isDeclaration,
                 message: '$cls must be the declaration.') &&
@@ skipping 482 matching lines @@
     // function expressions's element.
     // TODO(herhut): Generate classes for function expressions earlier.
     if (element is SynthesizedCallMethodElementX) {
       return getMightBePassedToApply(element.expression);
     }
     return functionsThatMightBePassedToApply.contains(element);
   }
 
   bool get hasClosedWorldAssumption => !compiler.hasIncrementalSupport;
 }