Display graphs of a web page inside a android webview?

Question

I have a problem, I want to show the graph in real time of a web page into a webview in my app. I tried the solution proposed How to display a part of the webpage on the webview android , but does not show anything in my app, could you help me to know where I am wrong? This is my code:

NOTE: To enter the webpage and see the graphs

User: javier

Password: 000000

public class MainActivity extends AppCompatActivity {
WebView mWebView;
Handler uiHandler = new Handler();
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    mWebView = (WebView)findViewById(R.id.activity_main_webview);

    //Activamos en JavaScript
    WebSettings webSettings = mWebView.getSettings();
    webSettings.setJavaScriptEnabled(true);
    //Activamos el zoom
    webSettings.setBuiltInZoomControls(true);
    mWebView.setWebViewClient(new MyWebViewClient());
    new BackgroundWorker().execute();
}

// load links in WebView instead of default browser
private class MyWebViewClient extends WebViewClient {

    @RequiresApi(21)
    @Override
    public boolean shouldOverrideUrlLoading(WebView view, WebResourceRequest request) {
        view.loadUrl(request.getUrl().toString());
        return false;
    }
}


private class BackgroundWorker extends AsyncTask<Void, Void, Void> {

    @Override
    protected Void doInBackground(Void... arg0) {
        getGraphics();
        return null;
    }

    public void getGraphics() {
        try {
            Document htmlDocument = Jsoup.connect("http://amunet.com.mx/wordpress/index.php/graficas-de-3-tomas/").get();
            Element element = htmlDocument.select("div#chartdiv1").first();


            // replace body with selected element
                htmlDocument.body().empty().append(element.toString());

             final String html = htmlDocument.toString();

            uiHandler.post(new Runnable() {
                @Override
                public void run() {
                    mWebView.loadData(html, "text/html", "UTF-8");
                }
            });
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
    if(event.getAction()== KeyEvent.ACTION_DOWN){
        switch(keyCode){
            case KeyEvent.KEYCODE_BACK:
                if(mWebView.canGoBack()){
                    mWebView.goBack();
                }
                else{
                    finish();
                }
                return true;
        }
    }
    return super.onKeyDown(keyCode, event);
}
}