Move TypeMask.simplify to a test helper.

tests/compiler/dart2js/list_tracer_test.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.
 
 import 'package:expect/expect.dart';
 import "package:async_helper/async_helper.dart";
 import
     '../../../sdk/lib/_internal/compiler/implementation/types/types.dart'
     show ContainerTypeMask, TypeMask;
 
 import 'compiler_helper.dart';
 import 'parser_helper.dart';
-
+import 'type_mask_test_helper.dart';
 
 String generateTest(String listAllocation) {
   return """
 int anInt = 42;
 double aDouble = 42.5;
 
 class A {
   final field;
   var nonFinalField;
 
@@ skipping 177 matching lines @@
   var compiler = compilerFor(generateTest(allocation), uri,
                              allowErrors: false, allowWarnings: false);
   asyncTest(() => compiler.runCompiler(uri).then((_) {
     var typesTask = compiler.typesTask;
     var typesInferrer = typesTask.typesInferrer;
 
     checkType(String name, type) {
       var element = findElement(compiler, name);
       ContainerTypeMask mask = typesInferrer.getTypeOfElement(element);
       if (nullify) type = type.nullable();
-      Expect.equals(type, mask.elementType.simplify(compiler), name);
+      Expect.equals(type, simplify(mask.elementType, compiler), name);
     }
 
     checkType('listInField', typesTask.numType);
     checkType('listPassedToMethod', typesTask.numType);
     checkType('listReturnedFromMethod', typesTask.numType);
     checkType('listUsedWithCascade', typesTask.numType);
     checkType('listUsedInClosure', typesTask.numType);
     checkType('listPassedToSelector', typesTask.numType);
     checkType('listReturnedFromSelector', typesTask.numType);
     checkType('listUsedWithAddAndInsert', typesTask.numType);
@@ skipping 14 matching lines @@
     checkType('listPassedAsNamedParameter', typesTask.numType);
     checkType('listStoredInList', typesTask.uint31Type);
     checkType('listStoredInListButEscapes', typesTask.dynamicType);
 
     if (!allocation.contains('filled')) {
       checkType('listUnset', new TypeMask.nonNullEmpty());
       checkType('listOnlySetWithConstraint', new TypeMask.nonNullEmpty());
     }
   }));
 }