Move TypeMask.simplify to a test helper.

tests/compiler/dart2js/cpa_inference_test.dart

Index: tests/compiler/dart2js/cpa_inference_test.dart
diff --git a/tests/compiler/dart2js/cpa_inference_test.dart b/tests/compiler/dart2js/cpa_inference_test.dart
index dcf347bb9a2f025812a6d4b72e6fbf2d747f61d5..6ea07a30e49b2edcfe4979dfbe9ee059f6fa9399 100644
--- a/tests/compiler/dart2js/cpa_inference_test.dart
+++ b/tests/compiler/dart2js/cpa_inference_test.dart
@@ -11,6 +11,7 @@ import '../../../sdk/lib/_internal/compiler/implementation/inferrer/concrete_typ
 
 import "parser_helper.dart";
 import "compiler_helper.dart";
+import "type_mask_test_helper.dart";
 import 'dart:mirrors';
 
 /**
@@ -1571,7 +1572,7 @@ testConcreteTypeToTypeMask() {
                   new TypeMask.subclass(a));
 
     Expect.equals(
-        convert(singleton(b).union(singleton(d))).simplify(result.compiler),
+        simplify(convert(singleton(b).union(singleton(d))), result.compiler),
         new TypeMask.nonNullSubtype(a));
   });
 }