While width and height are presentational hints on canvas, they actually
map to the CSS aspect-ratio attribute, not to CSS width and height.
For this reason, we actually need to manually mark for relayout here.
Also import a WPT test that was flaky before this change.
This isn't a full fix, as the paint function does not handle this
either. But instead of getting the bitmap from the image source
immediately, follow the spec a bit more closely by creating the
CanvasPatern object with the ImageSource directly.
Fixes a crash for the 5 included WPT tests.
