проверить, установлен ли флаг переноса

, используя ответ @ Andriy, и этот ответ i удалось установить высоту contentSize в WKWebView и изменить его высоту.

здесь полный быстрый код 4:

    var neededConstraints: [NSLayoutConstraint] = []

    @IBOutlet weak var webViewContainer: UIView!
    @IBOutlet weak var webViewHeight: NSLayoutConstraint! {
        didSet {
            if oldValue != nil, oldValue.constant != webViewHeight.constant {
                view.layoutIfNeeded()
            }
        }
    }


   lazy var webView: WKWebView = {
        var source = """
var observeDOM = (function(){
    var MutationObserver = window.MutationObserver || window.WebKitMutationObserver,
        eventListenerSupported = window.addEventListener;

    return function(obj, callback){
        if( MutationObserver ){
            // define a new observer
            var obs = new MutationObserver(function(mutations, observer){
                if( mutations[0].addedNodes.length || mutations[0].removedNodes.length )
                    callback();
            });
            // have the observer observe foo for changes in children
            obs.observe( obj, { childList:true, subtree:true });
        }
        else if( eventListenerSupported ){
            obj.addEventListener('DOMNodeInserted', callback, false);
            obj.addEventListener('DOMNodeRemoved', callback, false);
        }
    };
})();

// Observe a specific DOM element:
observeDOM( document.body ,function(){
    window.webkit.messageHandlers.sizeNotification.postMessage({'scrollHeight': document.body.scrollHeight,'offsetHeight':document.body.offsetHeight,'clientHeight':document.body.clientHeight});
});

"""

        let script = WKUserScript(source: source, injectionTime: .atDocumentEnd, forMainFrameOnly: true)
        let controller = WKUserContentController()
        controller.addUserScript(script)
        controller.add(self, name: "sizeNotification")
        let configuration = WKWebViewConfiguration()
        configuration.userContentController = controller
        let this = WKWebView(frame: .zero, configuration: configuration)
        webViewContainer.addSubview(this)
        this.translatesAutoresizingMaskIntoConstraints = false
        this.scrollView.isScrollEnabled = false
        // constraint for webview when added to it's superview
        neededConstraints += NSLayoutConstraint.constraints(withVisualFormat: "H:|[web]|",
                                                            options: [],
                                                            metrics: nil,
                                                            views: ["web": this])
        neededConstraints += NSLayoutConstraint.constraints(withVisualFormat: "V:|[web]|",
                                                            options: [],
                                                            metrics: nil,
                                                            views: ["web": this])
        return this
    }()


    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        _  = webView // to create constraints needed for webView
        NSLayoutConstraint.activate(neededConstraints)
        let url = URL(string: "https://www.awwwards.com/")!
        let request = URLRequest(url: url)
        webView.load(request)
    }

    func userContentController(_ userContentController: WKUserContentController, didReceive message: WKScriptMessage) {
        if let body = message.body as? Dictionary,
            let scrollHeight = body["scrollHeight"],
            let offsetHeight = body["offsetHeight"],
            let clientHeight = body["clientHeight"] {
            webViewHeight.constant = scrollHeight
            print(scrollHeight, offsetHeight, clientHeight)
        }
    }