Build libstd etc. with debug info when Servo configured with --enable-debug
Change the mechanism behind summit-crash.html
Move FailureMsg contents into a cloneable struct
Add a helper for sending a message on task failure
Restore failure handling

We probably leak some threads and resources, e.g. when the script task crashes
and doesn't get a chance to send layout data back to layout to be deallocated.

Not tested with iframes yet.
Restore hard-fail mode
Use hard-fail for reftests
Find failure.html relative to exe path, not cwd
Use DOMString more consistently.
auto merge of #1690 : Ms2ger/servo/DOMStrings, r=jdm
auto merge of #1691 : kmcallister/servo/linked-failure, r=pcwalton

We probably leak some threads and resources, e.g. when the script task crashes and doesn't get a chance to send layout data back to layout to be deallocated.

Not tested with iframes yet.
Move DOMString into servo_util.
Add str.rs.
auto merge of #1694 : Ms2ger/servo/move-DOMString, r=SimonSapin
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.