Instead, compute them on demand. This affects ReplacedBox and its
subclasses.
This commit is centered around a new Box::auto_content_box_size
method. It returns a SizeWithAspectRatio representing the natural
size of a replaced element, or the size derived from attributes
for text input and textarea. These values are used when the
corresponding axis is auto or indefinite.
Although introducing this API choke-point for sizing replaced and
replaced-like elements was the main goal, it's notable that layout
becomes more robust in the face of dynamic changes due to reduced
potential for stale size values (at the cost of extra calculations
and allocations).
:heading() now matches based on a computed heading level, which is based
on the level of the tag (h1, h2, etc) and then modified by these two new
attributes.
I'm caching this heading level on HTMLHeadingElement, based on the dom
tree version. That's more invalidation than is actually needed, but it
saves us calculating it over and over when the document hasn't changed.
The failing test cases are:
- Implicit headingreset for modal dialogs which is apparently unspecced
and controversial.
- Not walking the flat tree properly. A flat tree ancestor of a
slot-assigned element is its slot, which is something we don't do
anywhere that I could find. I've made a note to look into this later.
We also don't implement the `ReflectRange` IDL attribute yet, which
means we're not clamping the read value of `headingOffset`.
Corresponds to:
e774e8e318
Details' contents matches a new details-content pseudo element.
Further work is required to make this pseudo-element behave per spec.
This pseudo should be element-backed per
https://drafts.csswg.org/css-pseudo/#element-backed
