servo: Merge #6841 - script: Squash duplicate animation tick events in the queue (from pcwalton:squash-animation-ticks); r=metajack

This prevents them from piling up endlessly if the JS
`requestAnimationFrame()` callback takes a long time to complete.

r? @jdm

Source-Repo: https://github.com/servo/servo
Source-Revision: 12c46ddd6131533454e353fa8fdd8cb4b517ffd0

servo/components/script/script_task.rs

@@ -665,8 +665,9 @@ impl ScriptTask {
             }
         };
 
-        // Squash any pending resize, reflow, and mouse-move events in the queue.
+        // Squash any pending resize, reflow, animation tick, and mouse-move events in the queue.
         let mut mouse_move_event_index = None;
+        let mut animation_ticks = HashSet::new();
         loop {
             match event {
                 // This has to be handled before the ResizeMsg below,
@@ -682,6 +683,13 @@ impl ScriptTask {
                 MixedMessage::FromConstellation(ConstellationControlMsg::Viewport(id, rect)) => {
                     self.handle_viewport(id, rect);
                 }
+                MixedMessage::FromConstellation(ConstellationControlMsg::TickAllAnimations(
+                        pipeline_id)) => {
+                    if !animation_ticks.contains(&pipeline_id) {
+                        animation_ticks.insert(pipeline_id);
+                        sequential.push(event);
+                    }
+                }
                 MixedMessage::FromConstellation(ConstellationControlMsg::SendEvent(
                         _,
                         MouseMoveEvent(_))) => {