Auto merge of #26594 - mrobinson:animationiteration, r=jdm

Implement animationiteration event

This event is triggered when an animation iterates. This change also
moves iteration out of style calculation to an "update animations" which
is the next part of having animation event handling match the HTML spec.

This change causes a few more tests to pass. Some of the other tests which
exercise this functionality require `animationstart` events.

---
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- [ ] These changes fix #___ (GitHub issue number if applicable)
- [x] There are tests for these changes

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components/script/script_thread.rs

@@ -149,7 +149,6 @@ use script_traits::{
 };
 use servo_atoms::Atom;
 use servo_config::opts;
-use servo_config::pref;
 use servo_url::{ImmutableOrigin, MutableOrigin, ServoUrl};
 use std::borrow::Cow;
 use std::cell::Cell;
@@ -1631,19 +1630,17 @@ impl ScriptThread {
     // TODO(mrobinson): This should also update the current animations to conform to
     // the HTML specification.
     fn update_animations_and_send_events(&self) {
-        for (_, document) in self.documents.borrow().iter() {
-            // Only update the time if it isn't being managed by a test.
-            if !pref!(layout.animations.test.enabled) {
-                document.update_animation_timeline();
-            }
-        }
-
         // We remove the events because handling these events might trigger
         // a reflow which might want to add more events to the queue.
         let events = self.animation_events.replace(Vec::new());
         for event in events.into_iter() {
             self.handle_transition_or_animation_event(&event);
         }
+
+        for (_, document) in self.documents.borrow().iter() {
+            let update = document.update_animation_timeline();
+            unsafe { ScriptThread::process_animations_update(update) };
+        }
     }
 
     fn categorize_msg(&self, msg: &MixedMessage) -> ScriptThreadEventCategory {
@@ -2947,6 +2944,7 @@ impl ScriptThread {
 
         let event_atom = match event.event_type {
             TransitionOrAnimationEventType::AnimationEnd => atom!("animationend"),
+            TransitionOrAnimationEventType::AnimationIteration => atom!("animationiteration"),
             TransitionOrAnimationEventType::TransitionCancel => atom!("transitioncancel"),
             TransitionOrAnimationEventType::TransitionEnd => atom!("transitionend"),
             TransitionOrAnimationEventType::TransitionRun => atom!("transitionrun"),