[scroll-animations-1] Also rerun style/layout for changed timeline ranges (#8704)

Fixes #8694.

Author: flackr

scroll-animations-1/Overview.bs

@@ -1051,12 +1051,20 @@ spec: cssom-view-1; type: dfn;
 	as step 1 of [=update animations and send events=].
 
 	During step 7.14.1 of the [HTML Processing Model](https://html.spec.whatwg.org/multipage/webappapis.html#processing-model-8),
-	any created [=scroll progress timelines=] or [=view progress timelines=] are collected into an <dfn export>initially stale</dfn> set.
-	After step 7.14.1 if there are any [=initially stale=] timelines, they update their current time,
-	the set of [=initially stale=] timelines is cleared and
+	any created [=scroll progress timelines=] or [=view progress timelines=] are collected into a <dfn export>stale timelines</dfn> set.
+	After step 7.14 if any timelines' [=named timeline ranges=] have changed,
+	these timelines are added to the [=stale timelines=] set.
+	If there are any [=stale timelines=], they now update their current time and associated ranges,
+	the set of [=stale timelines=] is cleared and
 	we run and we run an additional step to recalculate styles and update layout.
-	As we only gather stale timelines during the first style and layout calculation,
+
+	Note: We check for layout changes after dispatching any {{ResizeObserver}}s intentionally
+	to take programmatically sized elements into account.
+
+	Note: As we only gather stale timelines during the first style and layout calculation,
 	this can only directly cause one additional style recalculation.
+	Other APIs which require another update should be checked in the same step
+	and be updated at the same time.
 
 	Note: Without this additional round of style and layout,
 	[=initially stale=] timelines would remain stale
@@ -1072,7 +1080,7 @@ spec: cssom-view-1; type: dfn;
 	In other words, [=initially stale=] timelines are visible as such
 	through those APIs.
 
-	If the step 7.14 of the [HTML Processing Model](https://html.spec.whatwg.org/multipage/webappapis.html#processing-model-8)
+	If the final style and layout update
 	would result in a change of time for any [=scroll progress timelines=] or
 	[=view progress timelines=], they will not be re-sampled to reflect the
 	new offset until the next update of the rendering.