Cache last fontgroup. Style recalc on wikipedia/rust 66ms -> 41ms.
Add layers dependency to util crate. Fixes #3783.
Rename untraceable!() to no_jsmanaged_fields!(). References issue #3671
auto merge of #3773 : rclanan/servo/rename-untraceable, r=jdm
Update rust-layers for android build fix.
Merge pull request #3799 from glennw/update-layers

Update rust-layers and friends for android build fix.
auto merge of #3794 : glennw/servo/font-content-opt, r=pcwalton
Use WindowMethods to get native graphics metadata instead of
relying on azure. This is a prerequisite for the switch to glutin.

Tested on Linux, mac. Tested that android + cef build.
auto merge of #3795 : jdm/servo/utildeps, r=metajack
auto merge of #3800 : glennw/servo/native-gfx-metadata, r=mbrubeck

This is a prerequisite for glutin support.

Tested on Linux, mac. Tested that android + cef build.
Add missing Cargo.lock deps change.
Add an optional --debug-mozjs argument to `mach build` that enables a non-optimized, debug build of mozjs and rust-mozjs. Update the Cargo snapshot to enable new feature support.
auto merge of #3803 : jdm/servo/mozjsdebug, r=mbrubeck

...n-optimized, debug build of mozjs and rust-mozjs. Update the Cargo snapshot to enable new feature support.
Mark the append_style reftest as flaky until we get better reliability. Fixes #3805.
auto merge of #3801 : jdm/servo/utildeps2, r=mbrubeck
auto merge of #3806 : jdm/servo/appendintermittent, r=Ms2ger

...Fixes #3805.
Customize RefCell instead of wrapping it

This gets rid of a dubious transmute:

    let val = mem::transmute::<&RefCell<T>, &T>(&self.base);

The code duplication will be reduced once rust-lang/rust#18131 is fixed.
Fix a layout method to use borrow_for_layout()
Dynamically check DOMRefCell access from layout in debug builds
Ignore the HTML parser's borrow flag in GC tracing

Adds some other dynamic checks in debug builds.