Move TypeMask.simplify to a test helper.

tests/compiler/dart2js/analyze_unused_dart2js_test.dart

Index: tests/compiler/dart2js/analyze_unused_dart2js_test.dart
diff --git a/tests/compiler/dart2js/analyze_unused_dart2js_test.dart b/tests/compiler/dart2js/analyze_unused_dart2js_test.dart
index e05a62c9c854d5f101eba90e4afd6a85f9fc18ea..26309d0cdc2cab85a7ad8c2dc81a7bcf173a0c86 100644
--- a/tests/compiler/dart2js/analyze_unused_dart2js_test.dart
+++ b/tests/compiler/dart2js/analyze_unused_dart2js_test.dart
@@ -12,15 +12,8 @@ import 'analyze_helper.dart';
 
 const String SIMPLIFY_NEVER_CALLED = "The method 'simplify' is never called";
 
-// The simplify method isn't used in dart2js anymore but is used by many tests.
-const Map<String, List<String>> WHITE_LIST = const {
-  "type_mask.dart": const [SIMPLIFY_NEVER_CALLED],
-  "concrete_types_inferrer.dart": const [SIMPLIFY_NEVER_CALLED],
-};
-
 void main() {
   var uri = currentDirectory.resolve(
       'sdk/lib/_internal/compiler/implementation/use_unused_api.dart');
-  asyncTest(
-      () => analyze([uri], WHITE_LIST, analyzeAll: false));
+  asyncTest(() => analyze([uri], {}, analyzeAll: false));
 }