style: Part 8: Hook scroll-timeline rule into Cascade data and use it for CSS animations

We hook the rule into cascade data, and so we can look it up by timeline
name. Now we only use StyleScrollDirection from @scroll-timeline rule.
`source` and `scroll-offsets` are skipped now and use the default values
instead because I'm pretty sure the syntax will be changed in Bug 1733260,
and `scroll-offsets` may be obsolete because the spec proposal intents to
make it be always 0% ~ 100%.

Also, add some reftests for the default `source` and `scroll-offsets`,
and different `orientation`s.

Besides, we disable at-scroll-timeline-start-end.html in Gecko because
we don't support start/end descriptors, and there are too many
intermittents in it.

Differential Revision: https://phabricator.services.mozilla.com/D126452

1 files changed, 6 insertions, 5 deletions

diff --git a/components/style/invalidation/stylesheets.rs b/components/style/invalidation/stylesheets.rs
index fc39b8cca76..1d1111170ed 100644
--- a/components/style/invalidation/stylesheets.rs
+++ b/components/style/invalidation/stylesheets.rs
@@ -619,11 +619,12 @@ impl StylesheetInvalidationSet {
                     // existing elements.
                 }
             },
-            ScrollTimeline(..) => {
-                // TODO: Bug 1676784: check if animation-timeline name is referenced.
-                // Now we do nothing.
-            },
-            CounterStyle(..) | Page(..) | Viewport(..) | FontFeatureValues(..) => {
+            // TODO: Check if timeline name is referenced, though this might go away in bug 1737918.
+            ScrollTimeline(..) |
+            CounterStyle(..) |
+            Page(..) |
+            Viewport(..) |
+            FontFeatureValues(..) => {
                 debug!(
                     " > Found unsupported rule, marking the whole subtree \
                      invalid."