The paintable tree structure more closely matches the painting order
when fragments are owned by corresponding inline paintables. This
change does not affect the layout tree, as it is more convenient for
layout purposes to have all fragments owned by a block container in
one place.
Additionally, this improves performance significantly on pages with
many fragments, as we no longer have to walk the ancestor chain up
to the closest block container to determine if a fragment belongs
to an inline paintable.
This is a part of refactoring towards making the paintable tree
independent of the layout tree. Now, instead of transferring text
fragments from the layout tree to the paintable tree during the layout
commit phase, we allocate separate PaintableFragments that contain only
the information necessary for painting. Doing this also allows us to
get rid LineBoxes, as they are used only during layout.
This patch makes a few changes to the way we calculate line-height:
- `line-height: normal` is now resolved using metrics from the used
font (specifically, round(A + D + lineGap)).
- `line-height: calc(...)` is now resolved at style compute time.
- `line-height` values are now absolutized at style compute time.
As a consequence of the above, we no longer need to walk the DOM
ancestor chain looking for line-heights during style computation.
Instead, values are inherited, resolved and absolutized locally.
This is not only much faster, but also makes our line-height metrics
match those of other engines like Gecko and Blink.
After commit ff48b7333c, we remove shadow
roots from elements that are removed from the DOM. Setting a node's
shadow root to null also sets that shadow root's host to null. Thus, the
comment in Node::is_shadow_including_descendant_of that assumes the host
is always non-null is not true.
The test added here would previously crash when interacting with a node
that is a descendant of a removed shadow root.
