Including JS script tag src correctly with custom User-Agent words by changing it in WebView setting

My code is as follow:

        myWebView = new WebView(this);
        myWebView.getSettings().setJavaScriptEnabled(true);
        myWebView.getSettings().setBuiltInZoomControls(true);
        myWebView.getSettings().setUserAgentString("iTunes-AppleTV/5.1 (3; 8GB; dt:12)");
        System.out.println(android.os.Build.VERSION.SDK_INT);
        if(android.os.Build.VERSION.SDK_INT > android.os.Build.VERSION_CODES.ICE_CREAM_SANDWICH_MR1) {
            myWebView.getSettings().setAllowUniversalAccessFromFileURLs(true);
        }
        myWebView.setWebChromeClient(new WebChromeClient());
      
        js_url_string =
                " var script=document.createElement('script'); "
                + " script.setAttribute('type','text/javascript'); "
                + " script.setAttribute('src', 'http://trailers.apple.com/appletv/us/js/application.js'); "
                + " script.onload = function() { "
                + " var req = new XMLHttpRequest(); "
                + " var req_cnt = 0; "
                + " req.onreadystatechange = function() { "
                + "       try { "
                + "        gtkTV.dump(req.readyState); "
                + "        "
                + "           if(req.readyState == 4) { "
                + "            if(req.status == 200) { "
                + "                if (req_cnt == 1) {"
                + "                    var url = req.responseText.match(/http:.*js/); "
                + "                    req.open('GET', url, true); "
                + "                    req.send(null); "
                + "                    req_cnt += 1; "
                + "                } "
                + "                else if (req_cnt == 2) { "
                + "                       gtkTV.loadXML(gtkTV.parseXML(req.responseText)); "
                + "                } "
                + "                else { "
                + "                    gtkTV.dump('Unknown request'); "
                + "                } "
                + "            } "
                + "            else { "
                + "                gtkTV.dump(req.statusText); "
                + "            } "
                + "        } "
                + "    } "
                + "       catch(e){ "
                + "           req.abort(); "
                + "        gtkTV.dump('Loadpage error!'); "
                + "       } "
                + " }; "
                + " gtkTV.dump(atv.config.ROOT_URL); "
                + " req.open('GET', atv.config.ROOT_URL, true); "
                + " req.send(null); "
                + " req_cnt += 1; "
                + " }; "
                + " document.getElementsByTagName('head')[0].appendChild(script); ";
      
        myWebView.setWebViewClient(new WebViewClient() {
            @Override
            public void onPageFinished(WebView view, String url) {
                view.loadUrl("javascript:(function() { "
                        + " document.getElementByTagName = function(id) {"
                        + "     return document.getElementsByTagName(id);"
                        + " };"
                        + js_url_string
                        + "})()");
            }
        });
        myWebView.addJavascriptInterface(new MyAndroidJSInterface(this, MainActivity.class), "gtkTV");
        myWebView.loadUrl("file:///android_asset/tmp.html");

My goal was to make script tag work for src to send request and include an external JS with a custom User-Agent value. Unfortunately after I did some research on the internet, I could not find a solution for it and people always say it's not a bug but not allowed by FF. At the moment when I was planning to give up and tried some other ugly ways to do that, I found a post at the reference link and realized Damn! that I was using WebView and there are some methods I could use to do that ! Better late than never, ugh.

Reference links
http://developer.android.com/guide/webapps/webview.html