Split layout code into a separate crate.
Split compositing/pipeline/constellation code into separate crate.
Fix incorrect libcompositing dep.
Remove some into_owned calls.
Mark some unused fields.
Remove the pointer to the Rust object in Root.

It is already stored inside the jsref field.
Merge pull request #2729 from Ms2ger/warnings

Fix some build warnings in the script crate; r=jack
Fix typo
Merge pull request #2733 from tavva/fix-typo

Fix typo
Update wpt expectations, include XHR in the WPT run
Merge pull request #2730 from Manishearth/expectations_up

Update wpt expectations, include XHR in the WPT run
Update submodule pointer and code to match interface change.
Merge pull request #2738 from glennw/azure-update

Update submodule pointer and code to match interface change.
Merge pull request #2726 from jdm/layoutsplit

Split layout code into a separate crate.
Filter response headers
Fix wpt failure on responseType setter