The specification dictates quite quite idiosyncratic return values when
querying insets of positioned elements via getComputedStyle(). These
depend on whether or not the elements size was overconstrained. This
change adds a better implementation of that in preparation for returning
proper values for position: sticky.
During layout it is often useful, for various specification reasons, to
know if an element is the `<body>` element of an `<html>` element root. There
are a couple places where a brittle heuristic is used to detect `<body>`
elements. This information is going to be even more important to
properly handle `<html>` elements that inherit their overflow property from
their `<body>` children.
Implementing this properly requires updating the DOM wrapper interface.
This check does reach up to the parent of thread-safe nodes, but this is
essentially the same kind of operation that `parent_style()` does, so is
ostensibly safe.
This change should not change any behavior and is just a preparation
step for properly handle `<body>` overflow.
Script will only scroll if it detects that an element has a scrolling
box, so this change adds an implementation of the scroll area query to
Layout 2020. This allows some scrolling tests to start passing.
This change also updates all expected results in css-backgrounds and
cssom-view.
This change adds support for the <iframe> element to Layout 2020. In
addition, certain aspects of the implementation are made the same
between both layout systems.
This implementation is more-or-less on par with the one from layout_2013
and in some cases better. There are still some cases where we don't
return the correct "resolved value," but this is enough to test
animations and transitions.
This isn't correct yet, but it is necessary to give a value in order for
scrolling from script to work. Later this should give an accurate
content box response as well as work for non-root elements.
