This momentarily handles the CSS property "position: absolute;" in
combination with the properties "top" and "left", so that elements can
be placed anywhere on the page independently from their parents.
Statically positioned elements ignore absolute positioned elements when
calculating their position as they don't take up space.
This patch adds HTMLCanvasElement along with a LayoutCanvas object.
The DOM and layout parts are very similar to <img> elements.
The <canvas> element holds a Gfx::Bitmap which is sized according to
the "width" and "height" attributes on the element.
Calling .getContext("2d") on a <canvas> element gives you a context
object that draws into the underlying Gfx::Bitmap of the <canvas>.
The context weakly points to the <canvas> which allows it to outlive
the canvas element if needed.
This is really quite cool. :^)
