constructor(keys = {}) {
    this.keyStates = keys;

    /**
     * Whether combination includes key up
     * @type {boolean}
     */
    this.isEnding = false;

    this._keyAliases = undefined;
    this._ids = undefined;
  }
Creates a new KeyCombination instance
@param {Object.<ReactKeyName, Array.<KeyEventState[]>>} keys Dictionary
       of keys
@returns {KeyCombination}