replaceState(oldState, newState) {
    return new FallThroughState(
        State.replaceStateId(this.id, oldState, newState),
        State.replaceStateId(this.fallThroughState, oldState, newState),
        this.statements);
  }
@param {number} oldState
@param {number} newState
@return {FallThroughState}