It seems that the source needs to be at a URL for it to work using loadURL(). Maybe it would work on a device and not in test movie? In any case, another way to go, that does work in test movie, is to use loadString(). Try this with your test html embedded in the app:
import flash.net.URLRequest;
import flash.net.URLLoader;
import flash.events.Event;
var webView:StageWebView = new StageWebView();
webView.stage = this.stage;
webView.viewPort = new Rectangle( 0, 0, stage.stageWidth, stage.stageHeight );
var req:URLRequest = new URLRequest("viewad.html");
var ldr:URLLoader = new URLLoader();
ldr.addEventListener(Event.COMPLETE,loaded);
ldr.load(req);
function loaded(e:Event){
webView.loadString(e.target.data)
}
