Enable missed tests

pkg/analysis_server/test/src/plugin/test_all.dart

 // Copyright (c) 2017, 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.
 
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
 import 'notification_manager_test.dart' as notification_manager_test;
 import 'plugin_locator_test.dart' as plugin_locator_test;
+import 'plugin_manager_test.dart' as plugin_manager_test;
+import 'plugin_watcher_test.dart' as plugin_watcher_test;
 import 'result_collector_test.dart' as result_collector_test;
 import 'result_converter_test.dart' as result_converter_test;
 import 'result_merger_test.dart' as result_merger_test;
 
 main() {
   defineReflectiveSuite(() {
     notification_manager_test.main();
     plugin_locator_test.main();
+    plugin_manager_test.main();
+    plugin_watcher_test.main();
     result_collector_test.main();
     result_converter_test.main();
     result_merger_test.main();
   });
 }