Auto merge of #26308 - mrobinson:animation-events2, r=jdm,emilio

Add support for transitionrun events

These events are triggered as soon as a transition is added to the list
of running transitions. This will allow better test coverage while
reworking the transitions and animations processing model.

<!-- Please describe your changes on the following line: -->

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `___` with appropriate data: -->
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [ ] These changes fix #___ (GitHub issue number if applicable)

<!-- Either: -->
- [x] There are tests for these changes OR
- [ ] These changes do not require tests because ___

<!-- Also, please make sure that "Allow edits from maintainers" checkbox is checked, so that we can help you if you get stuck somewhere along the way.-->

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

components/script/dom/event.rs

@@ -647,6 +647,7 @@ fn invoke(
             atom!("animationiteration") => Some(atom!("webkitAnimationIteration")),
             atom!("animationstart") => Some(atom!("webkitAnimationStart")),
             atom!("transitionend") => Some(atom!("webkitTransitionEnd")),
+            atom!("transitionrun") => Some(atom!("webkitTransitionRun")),
             _ => None,
         } {
             let original_type = event.type_();

components/script/dom/macros.rs

@@ -498,6 +498,7 @@ macro_rules! global_event_handlers(
         event_handler!(toggle, GetOntoggle, SetOntoggle);
         event_handler!(transitioncancel, GetOntransitioncancel, SetOntransitioncancel);
         event_handler!(transitionend, GetOntransitionend, SetOntransitionend);
+        event_handler!(transitionrun, GetOntransitionrun, SetOntransitionrun);
         event_handler!(volumechange, GetOnvolumechange, SetOnvolumechange);
         event_handler!(waiting, GetOnwaiting, SetOnwaiting);
     )

components/script/dom/webidls/EventHandler.webidl

@@ -92,6 +92,7 @@ interface mixin GlobalEventHandlers {
 
 // https://drafts.csswg.org/css-transitions/#interface-globaleventhandlers-idl
 partial interface mixin GlobalEventHandlers {
+           attribute EventHandler ontransitionrun;
            attribute EventHandler ontransitionend;
            attribute EventHandler ontransitioncancel;
 };

components/script/script_thread.rs

@@ -2920,22 +2920,20 @@ impl ScriptThread {
         let js_runtime = self.js_runtime.rt();
         let node = unsafe { from_untrusted_node_address(js_runtime, unsafe_node) };
 
-        let idx = self
+        let node_index = self
             .transitioning_nodes
             .borrow()
             .iter()
             .position(|n| &**n as *const _ == &*node as *const _);
-        match idx {
-            Some(idx) => {
-                self.transitioning_nodes.borrow_mut().remove(idx);
-            },
+        let node_index = match node_index {
+            Some(node_index) => node_index,
             None => {
                 // If no index is found, we can't know whether this node is safe to use.
                 // It's better not to fire a DOM event than crash.
                 warn!("Ignoring transition end notification for unknown node.");
                 return;
             },
-        }
+        };
 
         if self.closed_pipelines.borrow().contains(&pipeline_id) {
             warn!("Ignoring transition event for closed pipeline.");
@@ -2943,12 +2941,17 @@ impl ScriptThread {
         }
 
         let event_atom = match event_type {
+            TransitionEventType::TransitionRun => atom!("transitionrun"),
             TransitionEventType::TransitionEnd => {
                 // Not quite the right thing - see #13865.
                 node.dirty(NodeDamage::NodeStyleDamaged);
+                self.transitioning_nodes.borrow_mut().remove(node_index);
                 atom!("transitionend")
             },
-            TransitionEventType::TransitionCancel => atom!("transitioncancel"),
+            TransitionEventType::TransitionCancel => {
+                self.transitioning_nodes.borrow_mut().remove(node_index);
+                atom!("transitioncancel")
+            },
         };
 
         let event_init = TransitionEventInit {