set(key, value, silent) {
    const values = this.values_ || (this.values_ = {});
    if (silent) {
      values[key] = value;
    } else {
      const oldValue = values[key];
      values[key] = value;
      if (oldValue !== value) {
        this.notify(key, oldValue);
      }
    }
  }
Sets a value.
@param {string} key Key name.
@param {*} value Value.
@param {boolean} [silent] Update without triggering an event.
@api