Add code to run more tests from test_all

pkg/analyzer/test/src/task/strong/test_all.dart

 // Copyright (c) 2016, 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 analyzer.test.src.task.strong.test_all;
-
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
 import 'checker_test.dart' as checker_test;
 import 'front_end_inference_test.dart' as front_end_inference_test;
 import 'inferred_type_test.dart' as inferred_type_test;
+import 'non_null_checker_test.dart' as non_null_checker_test;
 
-/// Utility for manually running all tests.
 main() {
   defineReflectiveSuite(() {
     checker_test.main();
     front_end_inference_test.main();
     inferred_type_test.main();
+    non_null_checker_test.main();
   }, name: 'strong');
 }