anchor.diff:  
     FileSystemAccess._();
   
  -  void setOverrideRoot(ws.WorkspaceRoot root) {
  -    assert(_root == null);
  -    _root = root;
  -  }
  -
  +  /**
  +   * Returns the full display path for an entry.
  +   */
     Future<String> getDisplayPath(chrome.Entry entry) {
       return chrome.fileSystem.getDisplayPath(entry);
     }
   
  +  /**
  +   * Restores the ProjectLocationManager and returns a future with its value,
  +   * based on a folder token.
  +   */
     Future<ProjectLocationManager> restoreManager(Spark spark, String folderToken) {
       return ProjectLocationManager.restoreManager(spark, folderToken)
           .then((ProjectLocationManager manager) {
  
positive.code:   WorkspaceRoot _root;
    WorkspaceRoot get root {
      if (_root == null) {
        _root = new MockWorkspaceRoot(location.entry);
      }
  
      return _root;
  
negative.code: 
  FileSystemAccess _fileSystemAccess;
  
  /**
   * Sets the used FileSystemAccess class, allowing overriding versions of the
   * filesystem
   */
  void setMockFilesystemAccess() {
    assert(_fileSystemAccess == null || _fileSystemAccess.root == null);
    _fileSystemAccess = new MockFileSystemAccess();
  }
  
  /**
   * Returns the current FilesystemAccess
   */
  FileSystemAccess get fileSystemAccess {
    if (_fileSystemAccess == null) {
      _fileSystemAccess = new FileSystemAccess._();
  