Fix error introduced by added import

pkg/analyzer/lib/src/analyzer_impl.dart

 // Copyright (c) 2013, 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 analyzer_impl;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:io';
 
+import 'package:analyzer/file_system/file_system.dart' show Folder;
 import 'package:analyzer/file_system/physical_file_system.dart';
 import 'package:analyzer/source/package_map_provider.dart';
 import 'package:analyzer/source/package_map_resolver.dart';
 import 'package:analyzer/source/pub_package_map_provider.dart';
 import 'package:analyzer/src/error_formatter.dart';
 import 'package:analyzer/src/generated/java_core.dart' show JavaSystem;
 import 'package:analyzer/src/generated/java_engine.dart';
 
 import '../options.dart';
 import 'generated/constant.dart';
 import 'generated/element.dart';
 import 'generated/engine.dart';
 import 'generated/error.dart';
 import 'generated/java_io.dart';
 import 'generated/sdk_io.dart';
 import 'generated/source_io.dart';
-import 'package:analyzer/file_system/file_system.dart';
 
 DirectoryBasedDartSdk sdk;
 
 /**
  * The maximum number of sources for which AST structures should be kept in the cache.
  */
 const int _MAX_CACHE_SIZE = 512;
 
 /// Analyzes single library [File].
 class AnalyzerImpl {
@@ skipping 409 matching lines @@
     }
   }
 
   @override
   void logInformation2(String message, Object exception) {
     if (log) {
       stdout.writeln(message);
     }
   }
 }