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

      request.onupgradeneeded = (event) => {
        reject(new Error('DB did not exist!'));
        const transaction = event.target.transaction;
        transaction.abort();
      };

      request.onsuccess = (event) => {
        /** @type {IDBDatabase} */
        const db = event.target.result;
        resolve(db);
      };

      request.onerror = (event) => {
        event.preventDefault();
        reject(request.error);
      };
    });
  }
@param {string} name The name of the database to open.
@return {!Promise<!IDBDatabase>} Resolved when the named DB has been
  opened.
@private