updateManifestImplementation(key, manifest) {
    const op = this.connection_.startReadWriteOperation(this.manifestStore_);
    const store = op.store();
    store.get(key).onsuccess = (e) => {
      store.put(manifest, key);
    };

    return op.promise();
  }
@param {number} key
@param {!shaka.extern.ManifestDB} manifest
@return {!Promise}
@protected