Request a directory.

@param {string} path - Directory path
@param {Object} options
@returns {Promise} Resolves with an object containing the status code,
body and content-type

@private
function (path/*, options*/) {
    return this._getFileId(path).then((id) => {
      let query, fields, data, etagWithoutQuotes, itemsMap;
      if (! id) {
        return Promise.resolve({statusCode: 404});
      }

      query = '\'' + id + '\' in parents';
      fields = 'items(downloadUrl,etag,fileSize,id,mimeType,title)';
      return this._request('GET', BASE_URL + '/drive/v2/files?'
          + 'q=' + encodeURIComponent(query)
          + '&fields=' + encodeURIComponent(fields)
          + '&maxResults=1000',
          {})
      .then((response) => {
        if (response.status !== 200) {
          return Promise.reject('request failed or something: ' + response.status);
        }

        try {
          data = JSON.parse(response.responseText);
        } catch(e) {
          return Promise.reject('non-JSON response from GoogleDrive');
        }

        itemsMap = {};
        for (const item of data.items) {
          etagWithoutQuotes = removeQuotes(item.etag);
          if (item.mimeType === GD_DIR_MIME_TYPE) {
            this._fileIdCache.set(path + item.title + '/', item.id);
            itemsMap[item.title + '/'] = {
              ETag: etagWithoutQuotes
            };
          } else {
            this._fileIdCache.set(path + item.title, item.id);
            itemsMap[item.title] = {
              ETag: etagWithoutQuotes,
              'Content-Type': item.mimeType,
              'Content-Length': item.fileSize
            };
          }
        }

        // FIXME: add revision of folder!
        return Promise.resolve({statusCode: 200, body: itemsMap, contentType: RS_DIR_MIME_TYPE, revision: undefined});
      });
    });
  }