"permissions": [
      "serial",
      "notifications",
      {"fileSystem": ["write", "retainEntries", "directory"]}
   ],
   "file_handlers": {
      "text": {
         "types": [
            "text/*"
         ]
      }

chrome.fileSystem.chooseEntry({type: "openDirectory"},     function() {
  console.log();
});

 chrome.fileSystem.getWritableEntry(chosenFileEntry,     function(writableFileEntry) {
    writableFileEntry.createWriter(function(writer) {
      writer.onerror = errorHandler;
      writer.onwriteend = callback;

    chosenFileEntry.file(function(file) {
      writer.write(file);
    });
  }, errorHandler);
});