static deleteDatabase_(name) {
    return new Promise((resolve, reject) => {
      const request = indexedDB.deleteDatabase(name);

      request.onsuccess = (event) => {
        resolve();
      };

      request.onerror = (event) => {
        event.preventDefault();
        resolve();
      };
    });
  }
@param {string} name The name of the database to delete.
@return {!Promise} Resolved when the named DB has been deleted.
@private