Move TypeMask.simplify to a test helper.

tests/compiler/dart2js/mirror_final_field_inferrer_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.
 
 // Test that final fields in @MirrorsUsed are still inferred.
 
 import 'package:expect/expect.dart';
 import "package:async_helper/async_helper.dart";
 import 'memory_compiler.dart' show compilerFor;
 import 'compiler_helper.dart' show findElement;
+import 'type_mask_test_helper.dart';
 
 const MEMORY_SOURCE_FILES = const <String, String> {
   'main.dart': """
 @MirrorsUsed(targets: 'field')
 import 'dart:mirrors';
 
 const field = 42;
 
 main() {
   return field;
 }
 """
 };
 
 void main() {
   var compiler = compilerFor(MEMORY_SOURCE_FILES);
   asyncTest(() => compiler.runCompiler(Uri.parse('memory:main.dart')).then((_) {
     var element = findElement(compiler, 'field');
     var typesTask = compiler.typesTask;
-    var typesInferrer = typesTask.typesInferrer;        
+    var typesInferrer = typesTask.typesInferrer;
     Expect.equals(typesTask.uint31Type,
-                  typesInferrer.getTypeOfElement(element).simplify(compiler),
+                  simplify(typesInferrer.getTypeOfElement(element), compiler),
                   'field');
   }));
 }