code: function _subtreeFilter(file, scope) {
          if (scope) {
              if (scope.isDirectory) {
                  // Dirs always have trailing slash, so we don't have to worry about being
                  // a substring of another dir name
                  return file.fullPath.indexOf(scope.fullPath) === 0;
              } else {
                  return file.fullPath === scope.fullPath;
              }
          }
          return true;
      }
docs: Checks that the file matches the given subtree scope. To fully check whether the file
  should be in the search set, use _inSearchScope() instead - a supserset of this.
  
  @param {!File} file
  @param {?FileSystemEntry} scope Search scope, or null if whole project
  @return {boolean}