Move TypeMask.simplify to a test helper.

tests/compiler/dart2js/simple_inferrer_try_catch_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 TypeMask;
 
 import 'compiler_helper.dart';
+import 'type_mask_test_helper.dart';
 
 const String TEST = """
 returnInt1() {
   var a = 42;
   try {
     a = 54;
   } catch (e){
   }
   return a;
 }
@@ skipping 146 matching lines @@
 void main() {
   Uri uri = new Uri(scheme: 'source');
   var compiler = compilerFor(TEST, uri);
   asyncTest(() => compiler.runCompiler(uri).then((_) {
     var typesTask = compiler.typesTask;
     var typesInferrer = typesTask.typesInferrer;
 
     checkReturn(String name, type) {
       var element = findElement(compiler, name);
       Expect.equals(type,
-          typesInferrer.getReturnTypeOfElement(element).simplify(compiler));
+          simplify(typesInferrer.getReturnTypeOfElement(element), compiler));
     }
 
     checkReturn('returnInt1', typesTask.uint31Type);
     checkReturn('returnInt2', typesTask.uint31Type);
     checkReturn('returnInt3', typesTask.uint31Type);
     checkReturn('returnInt4', typesTask.uint31Type);
     checkReturn('returnInt5', typesTask.uint31Type);
     checkReturn('returnInt6',
         new TypeMask.nonNullSubtype(compiler.intClass));
 
     var subclassOfInterceptor =
         findTypeMask(compiler, 'Interceptor', 'nonNullSubclass');
 
     checkReturn('returnDyn1', subclassOfInterceptor);
     checkReturn('returnDyn2', subclassOfInterceptor);
     checkReturn('returnDyn3', subclassOfInterceptor);
     checkReturn('returnDyn4', subclassOfInterceptor);
     checkReturn('returnDyn5', subclassOfInterceptor);
     checkReturn('returnDyn6', typesTask.dynamicType);
   }));
 }