Move TypeMask.simplify to a test helper.

tests/compiler/dart2js/simple_inferrer_and_or_test.dart

Index: tests/compiler/dart2js/simple_inferrer_and_or_test.dart
diff --git a/tests/compiler/dart2js/simple_inferrer_and_or_test.dart b/tests/compiler/dart2js/simple_inferrer_and_or_test.dart
index 19926f00f95269bf32af96cff9f785d8f61a8006..97531a6846a85da489047542b61f7fc5d85a6667 100644
--- a/tests/compiler/dart2js/simple_inferrer_and_or_test.dart
+++ b/tests/compiler/dart2js/simple_inferrer_and_or_test.dart
@@ -5,6 +5,7 @@
 import 'package:expect/expect.dart';
 import "package:async_helper/async_helper.dart";
 import 'compiler_helper.dart';
+import 'type_mask_test_helper.dart';
 
 const String TEST = """
 class X {}
@@ -64,7 +65,7 @@ void main() {
     checkReturn(String name, type) {
       var element = findElement(compiler, name);
       Expect.equals(type,
-          typesInferrer.getReturnTypeOfElement(element).simplify(compiler));
+          simplify(typesInferrer.getReturnTypeOfElement(element), compiler));
     }
 
     var subclassOfInterceptor =