This method scrolls the document content in the window by a user specified amount
in the vertical and horizontal directions. This will scroll from the current scroll
position. If the current scroll position is (10,10) and this method is called with
(0,25), then the new scroll position would be (10,35).
var box = scene.getBoxById("htmlBox");
if (box)
{
box.loadURL("http://www.cnn.com");
box.scrollBy(0, 50);
}