WebView set default 404 page and some security setting

WebView404.java

final String offlineMessageHtml = "DEFINE THIS";
final String timeoutMessageHtml = "DEFINE THIS";

WebView browser = (WebView) findViewById(R.id.webview);
browser.setNetworkAvailable(isConnected);
browser.setWebViewClient(new WebViewClient() {
    @Override
    public boolean shouldOverrideUrlLoading(WebView view, String url) {
        if (isConnected) {
            // return false to let the WebView handle the URL
            return false;
        } else {
            // show the proper "not connected" message
            view.loadData(offlineMessageHtml, "text/html", "utf-8");
            // return true if the host application wants to leave the current 
            // WebView and handle the url itself
            return true;
        }
    }
    @Override
    public void onReceivedError (WebView view, int errorCode, 
        String description, String failingUrl) {
        if (errorCode == ERROR_TIMEOUT) {
            view.stopLoading();  // may not be needed
            view.loadData(timeoutMessageHtml, "text/html", "utf-8");
        }
    }
});

WebViewSecurity.java

if (Build.VERSION.SDK_INT < Build.VERSION_CODES.JELLY_BEAN_MR1) {
    mWebView.removeJavascriptInterface("searchBoxJavaBridge_");
}