Browsers such as Chrome and Firefox apply an arbitrary scale to the
current font size if `normal` is used for `line-height`. Firefox uses
1.2 while Chrome uses 1.15. Let's go with the latter for now, it's
relatively easy to change if we ever want to go back on that decision.
This also requires updating the expectations for a lot of layout tests.
The upside of this is that it's a bit easier to compare our layout
results to other browsers', especially Chrome.
Before this change, we assigned the style sheet's location *after* its
content rules were parsed and added to it. This meant any `@import`s
would try to fetch their style sheet before they knew the URL they
should fetch it relative to.