code: function createUntitledDocument(counter, fileExt) {
          var filename = Strings.UNTITLED + "-" + counter + fileExt,
              fullPath = _untitledDocumentPath + "/" + filename,
              now = new Date(),
              file = new InMemoryFile(fullPath, FileSystem);
  
          FileSystem.addEntryForPathIfRequired(file, fullPath);
  
          return new DocumentModule.Document(file, now, "");
      }
docs: Creates an untitled document. The associated File has a fullPath that
  looks like /some-random-string/Untitled-counter.fileExt.
  
  @param {number} counter - used in the name of the new Document's File
  @param {string} fileExt - file extension of the new Document's File, including "."
  @return {Document} - a new untitled Document