This commit adds hooks to the Servo style traversal to avoid traversing all the
DOM for every restyle. Additionally it changes the behavior of the dirty flag to
be propagated top down, to prevent extra overhead when an element is dirtied.
This commit doesn't aim to change the behavior on Servo just yet, since Servo
might rely on a full bottom up reconstruction of the flows. I'll need to double
check and implement that separately.
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.
Currently when traversing a the tree to restyle, we look at whether a
given element to restyle is the root. This seems to always be the root
of the entire document, since we start our processing from the top. If
the current element being restyled is the root of the restyle, then we
use None as the parent node for restyling purposes.
In stylo we want to invoke restyling starting from an arbitrary node in
the document, not just the root of the document, so this change looks
for the parent element regardless of whether we're at the root of the
restyle.
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
