I am using Sencha Architect to develop my Sencha Touch App. Architect creates an app.html file which contains a bit of Javascript to check if the browser is webkit capable:
    <script type="text/javascript">
         if (!Ext.browser.is.WebKit) {
             alert("The current browser is unsupported.\n\nSupported browsers:\n" +
                 "Google Chrome\n" +
                 "Apple Safari\n" +
                 "Mobile Safari (iOS)\n" +
                 "Android Browser\n" +
                 "BlackBerry Browser"
However, when I use the Sencha SDK tools to build my app for production
sencha app build production
the landing page, index.html contains the Microloader which is responsible for loading the app, checking for delta updates, loading the Sencha framework and probably many other things, but does not contain any webkit browser checking.

How could I implement this kind of checking to make sure the user is using a Webkit browser? Since we're not directly loading the Sencha framework, I can't use the above browser checking code. I guess when then code snippet is run, Sencha hasn't loaded yet, hence why I get an 'undefined' javascript error.

Any ideas?