onInfoMessage (code, cb) {
    if (!this._infoListeners[code]) {
      this._infoListeners[code] = []
    }

    this._infoListeners[code].push(cb)
  }
Registers a new callback to be called when a matching info message is
received.

@param {number} code - from #WSv2.info
@param {Function} cb - callback