This patch introduces infrastructure for the rule tree, and constructs it.
We don't use it yet, nor have good heuristics for GC'ing it, but this should not
happen anymore once we store the rule node reference in the node.
I haven't messed up with memory orders because I want to do a try run with it,
then mess with them.
Take down the ApplicableDeclarationsCache, use the rule tree for doing the cascade.
As a follow-up, we could move all the data living under a mutex in the
SharedLayoutContext only in order to create the local context to the same place.
This should increase animation performance when there are multiple animations in
one page that happen to be on different threads.
This commit refactors the style crate to be completely independent of
the actual implementation and pseudo-elements supported.
This also adds a gecko backend which introduces parsing for the
anonymous box pseudo-elements[1], although there's still no way of
querying them.
https://mxr.mozilla.org/mozilla-central/source/layout/style/nsCSSAnonBoxList.h
The pipeline id stuff is currently unused. If someone needs it, they can add
an additional trait bound on their css error reporter to get the pipeline id.
We do a few things-here:
* Hoist non-layout-dependent fields in SharedLayoutData and LocalLayoutData into style/.
* Hoist parts of css/matching.rs into style/.
* Hoist parts of layout/animation.rs into style/animation.rs.
* Remove the duplicated-but-slightly-different definition of OpaqueNode.
