Move TypeMask.simplify to a test helper.

tests/compiler/dart2js/simple_inferrer_no_such_method_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 TEST1 = """
 class A {
   noSuchMethod(im) => 42;
 }
 
 class B extends A {
   foo();
 }
 
@@ skipping 74 matching lines @@
 """;
 
 main() {
   Uri uri = new Uri(scheme: 'source');
 
   checkReturn(MockCompiler compiler, String name, type) {
     var typesInferrer = compiler.typesTask.typesInferrer;
     var element = findElement(compiler, name);
     Expect.equals(
         type,
-        typesInferrer.getReturnTypeOfElement(element).simplify(compiler),
+        simplify(typesInferrer.getReturnTypeOfElement(element), compiler),
         name);
   }
 
   var compiler1 = compilerFor(TEST1, uri);
   asyncTest(() => compiler1.runCompiler(uri).then((_) {
     checkReturn(compiler1, 'test1', compiler1.typesTask.uint31Type);
     checkReturn(compiler1, 'test2',
         compiler1.typesTask.dynamicType.nonNullable());
     checkReturn(compiler1, 'test3', compiler1.typesTask.uint31Type);
     checkReturn(compiler1, 'test4', compiler1.typesTask.mapType);
@@ skipping 12 matching lines @@
     checkReturn(compiler2, 'test5', compiler2.typesTask.mapType);
 
     checkReturn(compiler2, 'test6', compiler2.typesTask.numType);
     checkReturn(compiler2, 'test7', compiler2.typesTask.uint31Type);
     checkReturn(compiler2, 'test8', compiler2.typesTask.uint31Type);
     checkReturn(compiler2, 'test9', compiler2.typesTask.uint31Type);
     checkReturn(compiler2, 'test10', compiler2.typesTask.numType);
     checkReturn(compiler2, 'test11', compiler2.typesTask.doubleType);
   }));
 }