Move TypeMask.simplify to a test helper.

tests/compiler/dart2js/simple_inferrer_postfix_prefix_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 'compiler_helper.dart';
 import 'parser_helper.dart';
+import 'type_mask_test_helper.dart';
 
 const String TEST = """
 
 class A {
   get foo => 'string';
   set foo(value) {}
   operator[](index) => 'string';
   operator[]=(index, value) {}
 
   returnDynamic1() => foo--;
@@ skipping 46 matching lines @@
   Uri uri = new Uri(scheme: 'source');
   var compiler = compilerFor(TEST, uri);
   asyncTest(() => compiler.runCompiler(uri).then((_) {
     var typesTask = compiler.typesTask;
     var typesInferrer = typesTask.typesInferrer;
 
     checkReturnInClass(String className, String methodName, type) {
       var cls = findElement(compiler, className);
       var element = cls.lookupLocalMember(methodName);
       Expect.equals(type,
-          typesInferrer.getReturnTypeOfElement(element).simplify(compiler),
+          simplify(typesInferrer.getReturnTypeOfElement(element), compiler),
           methodName);
     }
 
     var subclassOfInterceptor =
         findTypeMask(compiler, 'Interceptor', 'nonNullSubclass');
 
     checkReturnInClass('A', 'returnNum1', typesTask.numType);
     checkReturnInClass('A', 'returnNum2', typesTask.numType);
     checkReturnInClass('A', 'returnNum3', typesTask.numType);
     checkReturnInClass('A', 'returnNum4', typesTask.numType);
     checkReturnInClass('A', 'returnEmpty1', const TypeMask.nonNullEmpty());
     checkReturnInClass('A', 'returnEmpty2', const TypeMask.nonNullEmpty());
     checkReturnInClass('A', 'returnDynamic1', subclassOfInterceptor);
     checkReturnInClass('A', 'returnDynamic2', subclassOfInterceptor);
     checkReturnInClass('A', 'returnEmpty3', const TypeMask.nonNullEmpty());
 
     checkReturnInClass('B', 'returnString1', typesTask.stringType);
     checkReturnInClass('B', 'returnString2', typesTask.stringType);
     checkReturnInClass('B', 'returnDynamic1', const TypeMask.nonNullEmpty());
     checkReturnInClass('B', 'returnDynamic2', const TypeMask.nonNullEmpty());
     checkReturnInClass('B', 'returnDynamic3', const TypeMask.nonNullEmpty());
     checkReturnInClass('B', 'returnDynamic4', const TypeMask.nonNullEmpty());
   }));
 }