code: function(db, trans, is_caller_setversion) {
  
      var action = is_caller_setversion ? 'changing' : 'upgrading';
      goog.log.finer(me.logger, action + ' version to ' + db.version +
          ' from ' + old_version);
  
      // create store that we don't have previously
      for (var i = 0; i < schema.stores.length; i++) {
        // this is sync process.
        me.update_store_(db, trans, schema.stores[i]);
      }
  
      // delete stores
      var storeNames = /** @type {DOMStringList} */ (db.objectStoreNames);
      for (var n = storeNames.length, i = 0; i < n; i++) {
        if (!schema.hasStore(storeNames[i])) {
          db.deleteObjectStore(storeNames[i]);
          goog.log.finer(me.logger, 'store: ' + storeNames[i] + ' deleted.');
        }
      }
    }
docs: Migrate from current version to the given version.
  @protected
  @param {IDBDatabase} db database instance.
  @param {IDBTransaction} trans transaction.
  @param {boolean} is_caller_setversion call from set version.