WebView crashing with BadTokenException when tapping SELECT item

Question

I (think I) have the same problem as described in this SO and also this SO :

I have a WebView in an TabGroupActivity. When I load a remote URL containing a SELECT element, and I tap on it, it crashes on my Nexus S running Android 4.1.2 (and I read the same reports from a user running a Samsung Galaxy S2 on 5.1.1 and a Nexus 5 on 6.0.0).

The exception is:

android.view.WindowManager$BadTokenException: Unable to add window -- token android.app.LocalActivityManager$LocalActivityRecord@4160b960 is not valid; is your activity running?

This is the structure:

// MobileWebTab.java
public class MobileWebTab extends TabGroupActivity {
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        startChildActivity("Mobile_Activity", new Intent(this,Mobile_Web_Activity.class));
    }
}

// Mobile_Web_Activity.java
public class Mobile_Web_Activity extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_mobile_web);
    } 
}


// MobileWebView.java
public class MobileWebView extends RelativeLayout {
    Context _context;
    private void initializeView(Context context){
        _context=context;
        LayoutInflater layoutInflater = LayoutInflater.from(context);
        layoutInflater.inflate(R.layout.layout_mobile_site, this);

        WebView mWebview  = (WebView)findViewById(R.id.ww_mobile_site);

        mWebview.setWebViewClient(new WebViewClient() {
                    //If you will not use this method url links are opeen in new brower not in webview
                    public boolean shouldOverrideUrlLoading(WebView view, String url) {
                        view.loadUrl(url);
                        return true;
                    }
        });
        mWebview.getSettings().setJavaScriptEnabled(true); // enable javascript

        mWebview.loadUrl(Constants.app_mobile_site);
    }

    public MobileWebView(Context context) {
        super(context);
        initializeView(context);
    }
    public MobileWebView(Context context, AttributeSet attrs) {
        super(context, attrs);
        initializeView(context);
    }

    public MobileWebView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        initializeView(context);
    }
}

Both answers recommend to set the parent activity context for the WebView - but how and where do I do that, when the WebView is defined via XML?