Use AbsolutePathContext in Folder.contains().

pkg/analyzer/lib/file_system/memory_file_system.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 memory_file_system;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:core' hide Resource;
 
 import 'package:analyzer/src/generated/engine.dart' show TimestampedData;
 import 'package:analyzer/src/generated/source_io.dart';
+import 'package:analyzer/src/util/absolute_path.dart';
 import 'package:path/path.dart';
 import 'package:watcher/watcher.dart';
 
 import 'file_system.dart';
 
 /**
  * An in-memory implementation of [ResourceProvider].
  * Use `/` as a path separator.
  */
 class MemoryResourceProvider implements ResourceProvider {
   final Map<String, _MemoryResource> _pathToResource =
       new HashMap<String, _MemoryResource>();
   final Map<String, String> _pathToContent = new HashMap<String, String>();
   final Map<String, int> _pathToTimestamp = new HashMap<String, int>();
   final Map<String, List<StreamController<WatchEvent>>> _pathToWatchers =
       new HashMap<String, List<StreamController<WatchEvent>>>();
   int nextStamp = 0;
 
+  final AbsolutePathContext absolutePathContext =
+      new AbsolutePathContext(posix.separator);
+
   @override
   Context get pathContext => posix;
 
   /**
    * Delete the file with the given path.
    */
   void deleteFile(String path) {
     _checkFileAtPath(path);
     _pathToResource.remove(path);
     _pathToContent.remove(path);
     _pathToTimestamp.remove(path);
     _notifyWatchers(path, ChangeType.REMOVE);
   }
 
   /**
    * Delete the folder with the given path
-   * and recurively delete nested files and folders.
+   * and recursively delete nested files and folders.
    */
   void deleteFolder(String path) {
     _checkFolderAtPath(path);
     _MemoryFolder folder = _pathToResource[path];
     for (Resource child in folder.getChildren()) {
       if (child is File) {
         deleteFile(child.path);
       } else if (child is Folder) {
         deleteFolder(child.path);
       } else {
@@ skipping 428 matching lines @@
   bool operator ==(other) {
     if (runtimeType != other.runtimeType) {
       return false;
     }
     return path == other.path;
   }
 
   @override
   String toString() => path;
 }