public class MainActivity extends AppCompatActivity
    implements NavigationView.OnNavigationItemSelectedListener {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    if(null == savedInstanceState) {
        // set you initial fragment object
        FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
        transaction.replace(R.id.content, InicioPagina.newInstance());
        transaction.commit();
    }

public class InicioPagina extends Fragment {

private ProgressBar prg;
SwipeRefreshLayout mySwipeRefreshLayout;
public WebView myWebView;

public static InicioPagina newInstance() {
    InicioPagina fragment = new InicioPagina();
    return fragment;
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.iniciopagina, container, false);
    prg = (ProgressBar)rootView.findViewById(R.id.progressBar2);
    mySwipeRefreshLayout = (SwipeRefreshLayout) rootView.findViewById(R.id.swipelayout);
    myWebView = (WebView) rootView.findViewById(R.id.inicio_pagina);
    myWebView.loadUrl("http://example.com.br/");

    //*Ativar JavaScript
    WebSettings webSettings = myWebView.getSettings();
    webSettings.setJavaScriptEnabled(true);

    //*Forçar links para abrir no WebView ao invés do navegador
    myWebView.setWebViewClient(new WebViewClient());


    myWebView.setVerticalScrollBarEnabled(false);

    mySwipeRefreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
        @Override
        public void onRefresh() {
            myWebView.reload();
            mySwipeRefreshLayout.setRefreshing(false);
        }
    });

    myWebView.setOnKeyListener(new View.OnKeyListener()
    {
        @Override
        public boolean onKey(View v, int keyCode, KeyEvent event)
        {
            if(event.getAction() == KeyEvent.ACTION_DOWN)
            {
                WebView webView = (WebView) v;

                switch(keyCode)
                {
                    case KeyEvent.KEYCODE_BACK:
                        if(webView.canGoBack())
                        {
                            webView.goBack();
                            return true;
                        }
                        break;
                }
            }

            return false;
        }
    });

    return rootView;
}

public class WebViewClient extends android.webkit.WebViewClient{
    @Override
    public void onPageStarted(WebView view, String url, Bitmap favicon) {
        prg.setVisibility(View.VISIBLE);
        super.onPageStarted(view, url, favicon);
    }
    @Override
    public void onPageFinished(WebView view, String url) {
        prg.setVisibility(View.GONE);

        super.onPageFinished(view, url);
    }
}

<android.support.constraint.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
tools:showIn="@layout/app_bar_main"
tools:context="br.com.example.example.MainActivity">
<RelativeLayout
    android:layout_width="wrap_content"
    android:layout_height="wrap_content">
        <FrameLayout
            android:id="@+id/content"
            android:layout_width="match_parent"
            android:layout_height="match_parent"></FrameLayout>
</RelativeLayout>

<TextView
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="Sem acesso a internet"
    android:textAlignment="center"
    android:textSize="30sp" />