Move TypeMask.simplify to a test helper.

tests/compiler/dart2js/type_mask_test_helper.dart

Index: tests/compiler/dart2js/type_mask_test_helper.dart
diff --git a/tests/compiler/dart2js/type_mask_test_helper.dart b/tests/compiler/dart2js/type_mask_test_helper.dart
new file mode 100644
index 0000000000000000000000000000000000000000..88f234da64c95cbdfd23b2b3d6df1cc12132c58c
--- /dev/null
+++ b/tests/compiler/dart2js/type_mask_test_helper.dart
@@ -0,0 +1,19 @@
+// 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.
+
+library type_mask_test_helper;
+
+import '../../../sdk/lib/_internal/compiler/implementation/types/types.dart';
+import '../../../sdk/lib/_internal/compiler/implementation/dart2jslib.dart'
+    show Compiler;
+
+TypeMask simplify(TypeMask mask, Compiler compiler) {
+  if (mask is ForwardingTypeMask) {
+    return simplify(mask.forwardTo, compiler);
+  } else if (mask is UnionTypeMask) {
+    return UnionTypeMask.flatten(mask.disjointMasks, compiler);
+  } else {
+    return mask;
+  }
+}