Update web-platform-tests expected results.
Order of firing events
auto merge of #2526 : Manishearth/servo/event-order, r=Ms2ger

For the wpt test [event_load](https://github.com/w3c/web-platform-tests/blob/master/XMLHttpRequest/event-load.htm)

Blocks #2525
Remove needless '&mut self' from WindowMethods.
Remove needless '&mut self' from DocumentMethods.
auto merge of #2556 : Ms2ger/servo/update-wpt, r=metajack
Move WebIDL unions into their own module.

This will allow multiple unions to contain the same type.
auto merge of #2558 : Ms2ger/servo/mod-unions, r=jdm

This will allow multiple unions to contain the same type.
auto merge of #2557 : saneyuki/servo/mut, r=jdm

related #2514
layout: Reference count flows, and forbid unsafe code in many places.
auto merge of #2570 : pcwalton/servo/ref-count-flows, r=pcwalton

r? @glennw
Add responseText and status code support to XHR
auto merge of #2521 : Manishearth/servo/xhr-responsetext, r=Ms2ger

Blocks #2282
Remove all old layers when creating a new root.

Fixes #2259.
Check the pipeline ID of the new root layer.

This isn't related to any known issue, but is just to ensure that the IDs are
set correctly within this function.
Remove unused delete_layer code.
auto merge of #2575 : mbrubeck/servo/2259-remove-old-layers, r=pcwalton

This fixes #2259 which was caused by some of the previous layers sticking around incorrectly.  Depends on mozilla-servo/rust-layers#69.

Also includes some related cleanup as separate commits.

No reftest because our test harness doesn't yet support navigating to a new page (#2574).
Minor style cleanups in Cache code

- Make ApplicableDeclarationsCache::cache priv
- Add a missing semicolon for clarity
- Remove a useless `drop` call.
Minor code cleanup in css::matching
Fix deriving in cascade_with_cached_declarations

Even though we don't recompute non-inherited properties here, we still need
to compute properties that are derived from them.  Fixes #2498: because
text-decoration is not inherited, -servo-text-decorations-in-effect was not
derived correctly for cached declarations.