@Override
public boolean shouldOverrideUrlLoading(WebView view, String url) {
    Uri uri= Uri.parse(url);

    if (uri.getScheme().equals("dmevent")) {
        String event = uri.getQueryParameter("event");

        switch (event) {
            case "ad_start":

                // The ad has started playing

                break;
            case "ad_end":

                // The ad is over

                break;
            }

            return true;
        }

        return super.shouldOverrideUrlLoading(view, url);
    }