Revert breaking change

pkg/analyzer/test/test_all.dart

 // Copyright (c) 2014, 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 test.engine;
 
 import 'package:unittest/unittest.dart';
 
 import 'cancelable_future_test.dart' as cancelable_future_test;
 import 'enum_test.dart' as enum_test;
 import 'file_system/test_all.dart' as file_system;
 import 'generated/test_all.dart' as generated;
 import 'instrumentation/test_all.dart' as instrumentation;
 import 'parse_compilation_unit_test.dart' as parse_compilation_unit;
+import 'plugin/test_all.dart' as plugin_test_all;
 import 'source/test_all.dart' as source;
 import 'src/test_all.dart' as src;
 import 'task/test_all.dart' as task;
 
 /// Utility for manually running all tests.
 main() {
   groupSep = ' | ';
   group('analysis engine', () {
     cancelable_future_test.main();
     enum_test.main();
     file_system.main();
     generated.main();
     instrumentation.main();
     parse_compilation_unit.main();
+    plugin_test_all.main();
     source.main();
     src.main();
     task.main();
   });
 }