static createV1_(db) {
    const StorageMechanism = shaka.offline.indexeddb.StorageMechanism;
    const segmentStore = StorageMechanism.V1_SEGMENT_STORE;
    const manifestStore = StorageMechanism.V1_MANIFEST_STORE;
    const stores = db.objectStoreNames;
    if (stores.contains(manifestStore) && stores.contains(segmentStore)) {
      shaka.log.debug('Mounting v1 idb storage cell');

      return new shaka.offline.indexeddb.V1StorageCell(
          db,
          segmentStore,
          manifestStore);
    }
    return null;
  }
@param {!IDBDatabase} db
@return {shaka.extern.StorageCell}
@private