Revert breaking change

pkg/analyzer/test/src/task/dart_test.dart

 // Copyright (c) 2015, 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.src.task.dart_test;
 
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/file_system/memory_file_system.dart';
+import 'package:analyzer/plugin/plugin.dart';
+import 'package:analyzer/plugin/task.dart';
 import 'package:analyzer/src/context/cache.dart';
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart';
 import 'package:analyzer/src/generated/engine.dart'
     hide AnalysisTask, GetContentTask, ParseDartTask, ScanDartTask;
 import 'package:analyzer/src/generated/error.dart';
 import 'package:analyzer/src/generated/resolver.dart';
 import 'package:analyzer/src/generated/sdk.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/plugin/engine_plugin.dart';
+import 'package:analyzer/src/plugin/plugin_impl.dart';
 import 'package:analyzer/src/task/dart.dart';
 import 'package:analyzer/src/task/driver.dart';
 import 'package:analyzer/src/task/manager.dart';
 import 'package:analyzer/task/dart.dart';
 import 'package:analyzer/task/general.dart';
 import 'package:analyzer/task/model.dart';
-import 'package:plugin/manager.dart';
 import 'package:typed_mock/typed_mock.dart';
 import 'package:unittest/unittest.dart';
 
 import '../../generated/test_support.dart';
 import '../../reflective_tests.dart';
 import '../mock_sdk.dart';
 
 main() {
   groupSep = ' | ';
   runReflectiveTests(BuildClassConstructorsTaskTest);
@@ skipping 1877 matching lines @@
     return entryMap.putIfAbsent(target, () => new CacheEntry());
   }
 
   TimestampedData<String> getContents(Source source) => source.contents;
 
   noSuchMethod(Invocation invocation) {
     print('noSuchMethod: ${invocation.memberName}');
     return super.noSuchMethod(invocation);
   }
 }