Fix typo in TypeInformationSystem.joinTypeMasks

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

 // Copyright (c) 2013, 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 type_graph_inferrer;
 
 import 'dart:collection' show Queue;
 
 import '../common.dart';
 import '../common/names.dart' show
@@ skipping 535 matching lines @@
     for (TypeMask mask in masks) {
       // Don't do any work on computing unions if we know that after all that
       // work the result will be `dynamic`.
       // TODO(sigmund): change to `mask == dynamicType` so we can continue to
       // track the non-nullable bit.
       if (mask.containsAll(classWorld)) return dynamicType;
       list.add(mask);
     }
 
     TypeMask newType = null;
-    for (TypeMask mask in masks) {
+    for (TypeMask mask in list) {
       newType = newType == null ? mask : newType.union(mask, classWorld);
       // Likewise - stop early if we already reach dynamic.
       if (newType.containsAll(classWorld)) return dynamicType;
     }
 
     return newType ?? const TypeMask.nonNullEmpty();
   }
 }
 
 /**
@@ skipping 856 matching lines @@
   bool isCalledOnce(Element element) {
     if (compiler.disableTypeInference) return false;
     MemberTypeInformation info = inferrer.types.getInferredTypeOf(element);
     return info.isCalledOnce();
   }
 
   void clear() {
     inferrer.clear();
   }
 }