persist_() {
    var putTx = this.db_.createTransaction(
        [e2e.ext.utils.IndexedDbStorage.OBJECTSTORE_NAME_],
        goog.db.Transaction.TransactionMode.READ_WRITE);
    putTx.objectStore(e2e.ext.utils.IndexedDbStorage.OBJECTSTORE_NAME_)
        .put(this.storage_, this.storageKey_);
  }
Persists the data in internal storage into IndexedDB.
@private