It used to be the case that MatchingContext was immutable and thus we didn't
care to have accessors.
This is no longer true, so let's make this code a bit nicer.
Right now we go through a lot of hoops to see if we ever see a relevant link.
However, that information is not needed: if the element is a link, we'll always
need to compute its visited style because its its own relevant link.
If the element inherits from a link, we need to also compute the visited style
anyway.
So the "has a relevant link been found" is pretty useless when we know what are
we inheriting from.
The branches at the beginning of matches_complex_selector_internal were
affecting performance, and there are no good reasons to keep them.
I've verified that this passes all the visited tests in mozilla central, and
that the test-cases too-flaky to be landed still pass.
This type is a lot of complexity related to a very specific thing such as the
hover and active quirk.
Instead of that, move `nesting_level` to `MatchingContext`, and simplify all
this computing whether the quirk applies upfront, for each complex selector we
test.
This is less error-prone, and also allows simplifying more stuff in a bit.
Otherwise, tests like the following fail, given we always match as unvisited,
and we'd never mark the link as needing invalidation.
<!doctype html>
<style>
a {
color: red !important;
}
.foo :visited {
color: green !important;
}
</style>
<div>
<a href="https://google.es">visit me</a>
<button onclick="this.parentNode.className = 'foo'">Then click me</button>
</div>
Bug: 1368240
MozReview-Commit-ID: LDv6S28c4ju
