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.
These allow accessing embeds, forms, images and objects with a given
name attribute, and any element with a given id attribute, as top level
properties on the global object.
It also allows accessing NavigableContainers by target name as top level
properties on the global object.
The current implementation feels very expensive. It's likely that
these values will need smarter caching in the future.
