Works:
mWebView.setWebViewClient(new WebViewClient() {
    @Override
    public boolean shouldOverrideUrlLoading(WebView view, String url) {
        view.loadUrl("file:///android_asset/www/css-js/app.css");
        return true;
    }
});
Doesn't Work:
mWebView.setWebViewClient(new WebViewClient() {
    @Override
    public boolean shouldOverrideUrlLoading(WebView view, String url) {
        view.loadUrl("http://yahoo.com");
        return true;
    }
});
 
    