cleanup LocalLibraryContributor

pkg/analysis_server/lib/src/services/completion/dart_completion_cache.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 services.completion.dart.cache;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:analysis_server/src/protocol_server.dart'
     hide Element, ElementKind;
 import 'package:analysis_server/src/services/completion/completion_manager.dart';
 import 'package:analysis_server/src/services/completion/dart_completion_manager.dart';
 import 'package:analysis_server/src/services/completion/suggestion_builder.dart';
 import 'package:analysis_server/src/services/search/search_engine.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
-import 'package:analyzer/dart/element/visitor.dart';
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/resolver.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/task/dart.dart';
 
 /**
  * The `DartCompletionCache` contains cached information from a prior code
  * completion operation.
  */
@@ skipping 321 matching lines @@
     if (libSource == source) {
       return new Future.value(unit);
     }
     // If [source] is a part, then compute the library unit
     if (libSource != null) {
       return context.computeResolvedCompilationUnitAsync(libSource, libSource);
     }
     return new Future.value(null);
   }
 }