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.
493dd5d93c caused the `::before`
pseudo-element node to be inserted before the element's content, which
caused issues with how we determine where to insert inline nodes into
the layout tree. At the time, I noticed the issue with contents of flex
containers, and prevented them from merging into a `::before` box.
However, a similar situation happens when we're not in a flex container,
but the pseudo-element has `display: block`. This commit fixes that
situation by using the same logic in both places, so a similar mistake
can't be made again.
This fixes the tab text being invisible on GitHub project pages. :^)
