Remove some dead code.
Rename make_url/current_url to parse_url/base_url, to align with spec terminology.
Remove unused Reflector::get_rootable.
auto merge of #1608 : SimonSapin/servo/url, r=metajack

Align with spec terminology.
auto merge of #1637 : Ms2ger/servo/get_rootable, r=pcwalton
Reduce copying on parse_url() call sites.
auto merge of #1642 : saneyuki/servo/1535, r=SimonSapin

this will fix #1535

r?
Rename "get_applicable_declarations" to "push_applicable_declarations".
auto merge of #1643 : saneyuki/servo/1641, r=SimonSapin

This will fix #1641
r?
style: Separate out style structs into inherited and initial structs.

This doesn't make much of a difference in performance, but will be
necessary for style struct sharing.
layout: Stop storing intermediate applicable declarations inside layout
data.

9% improvement in style recalc on the rainbow page.
layout: Implement basic style sharing.

No improvement on the rainbow page, but necessary for some other
optimizations we want to do.
layout: Cache applicable-declarations-to-computed-values mappings.

If the cache is hit, then we can only compute inherited properties. This
is a WebKit optimization.
style: Eliminate a temporary vector when performing selector matching.

26% improvement in style recalc on the rainbow page.
layout: Aggressively try to share styles with the last few nodes seen.

This roughly implements the same cache found in Blink. 50% improvement
on the rainbow page, but at the cost of reducing parallel gains down to
nothing. I added a new page, `perf-rainbow-hard.html`, which disables
the optimizations in both Blink and Servo.