asCanvasElement method
Ensures that DOM element to render is a canvas. If not will insert a canvas inside the element and use it.
Implementation
CanvasElement asCanvasElement(Element element) {
if (element is CanvasElement) return element;
var w = getElementWidth(element, 640);
var h = getElementHeight(element, 480);
var canvas = CanvasElement(width: w, height: h);
element.children.add(canvas);
return canvas;
}