add = (keyCode, keyCap, normal, control, alt, meta) => {
    this.addKeyDef(keyCode, {
      keyCap: keyCap,
      normal: normal,
      control: control,
      alt: alt,
      meta: meta,
    });
  }
@param {number} keyCode
@param {string} keyCap
@param {!hterm.Keyboard.KeyDefAction} normal
@param {!hterm.Keyboard.KeyDefAction} control
@param {!hterm.Keyboard.KeyDefAction} alt
@param {!hterm.Keyboard.KeyDefAction} meta