Add Folder.contains(path) and use it in ContextDirectoryManager.

pkg/analysis_server/lib/src/context_directory_manager.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 context.directory.manager;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:analyzer/file_system/file_system.dart';
@@ skipping 229 matching lines @@
     return file.exists;
   }
 
   /**
    * Returns `true` if the given absolute [path] is in one of the current
    * root folders and is not excluded.
    */
   bool isInAnalysisRoot(String path) {
     // TODO(scheglov) check for excluded paths
     for (Folder root in _currentDirectoryInfo.keys) {
-      if (path.startsWith(root.path)) {
+      if (root.contains(path)) {
         return true;
       }
     }
     return false;
   }
 
   /**
    * Called when a new context needs to be created.
    */
   void addContext(Folder folder, Map<String, List<Folder>> packageMap);
 
   /**
    * Called when the set of files associated with a context have changed (or
    * some of those files have been modified).  [changeSet] is the set of
    * changes that need to be applied to the context.
    */
   void applyChangesToContext(Folder contextFolder, ChangeSet changeSet);
 
   /**
    * Remove the context associated with the given [folder].
    */
   void removeContext(Folder folder);
 
   /**
    * Called when the package map for a context has changed.
    */
   void updateContextPackageMap(Folder contextFolder,
                                Map<String, List<Folder>> packageMap);
 }