Clean up some warnings (issue 25964)

pkg/analysis_server/test/services/completion/dart/completion_manager_test.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.services.completion.dart.manager;
 
 import 'dart:async';
 
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
 import 'package:analysis_server/src/services/completion/completion_core.dart';
 import 'package:analysis_server/src/services/completion/completion_performance.dart';
 import 'package:analysis_server/src/services/completion/dart/completion_manager.dart';
 import 'package:analysis_server/src/services/completion/dart/imported_reference_contributor.dart';
 import 'package:analyzer/dart/element/element.dart';
+import 'package:analyzer/src/task/dart.dart';
 import 'package:analyzer/task/dart.dart';
-import 'package:analyzer/src/task/dart.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 import 'package:unittest/unittest.dart';
 
 import '../../../utils.dart';
 import 'completion_contributor_util.dart';
-import 'package:analyzer/src/generated/source.dart';
 
 main() {
   initializeTestEnvironment();
   defineReflectiveTests(CompletionManagerTest);
 }
 
 @reflectiveTest
 class CompletionManagerTest extends DartCompletionContributorTest {
   @override
   DartCompletionContributor createContributor() {
@@ skipping 64 matching lines @@
     void assertImportedLib(String expectedUri) {
       ImportElement importElem = importNamed(expectedUri);
       expect(importElem.importedLibrary.exportNamespace, isNotNull);
     }
 
     // Assert that the new imports each have an export namespace
     assertImportedLib(null /* dart:core */);
     assertImportedLib('/libA.dart');
   }
 }