onOpen() {
        this.readyState = "open";
        Socket.priorWebsocketSuccess = "websocket" === this.transport.name;
        this.emitReserved("open");
        this.flush();
        // we check for `readyState` in case an `open`
        // listener already closed the socket
        if ("open" === this.readyState &&
            this.opts.upgrade &&
            this.transport.pause) {
            let i = 0;
            const l = this.upgrades.length;
            for (; i < l; i++) {
                this.probe(this.upgrades[i]);
            }
        }
    }
Called when connection is deemed open.

@api private