getState() {
    return {
      "s": this.snakeSquares_.slice(),
      "f": this.fruitSquares_.slice()
    }
  }
Get plain JavaScript representation of the game state.

@return An object with two keys:
  - s: {Array<[number, number]>} representing the squares occupied by
       the snake. The array is ordered in such a way that the first
       element corresponds to the head of the snake and the last
       element corresponds to the tail.
  - f: {Array<[number, number]>} representing the squares occupied by
       the fruit(s).