The box tree and line boxes now all store a relative offset from their
containing block, instead of an absolute (document-relative) position.
This removes a huge pain point from the layout system which was having
to adjust offsets recursively when something moved. It also makes some
layout logic significantly simpler.
Every box can still find its absolute position by walking its chain
of containing blocks and accumulating the translation from the root.
This is currently what we do both for rendering and hit testing.
This patch introduces support for more than just "absolute px" units in
our Length class. It now also supports "em" and "rem", which are units
relative to the font-size of the current layout node and the <html>
element's layout node respectively.
LayoutReplaced now has intrinsic width, height and ratio. Only some of
the values may be present. The layout algorithm takes the various
configurations into account per the CSS specification.
This is still pretty immature but at least we're moving forward. :^)
Previously we would only check if the border width property is empty and
skip drawing in that case, and enforcing a minimum width of 1px
otherwise - but "border: 0;" should not paint a border :^)
