4 files changed, 53 insertions, 7 deletions

diff --git a/dom/animation/Animation.cpp b/dom/animation/Animation.cpp
index 6dd583ed1e..cefdbb76d4 100644
--- a/dom/animation/Animation.cpp
+++ b/dom/animation/Animation.cpp
@@ -230,6 +230,10 @@ Animation::SetTimelineNoUpdate(AnimationTimeline* aTimeline)
     return;
   }
 
+  StickyTimeDuration activeTime = mEffect
+                                  ? mEffect->GetComputedTiming().mActiveTime
+                                  : StickyTimeDuration();
+
   RefPtr<AnimationTimeline> oldTimeline = mTimeline;
   if (oldTimeline) {
     oldTimeline->RemoveAnimation(this);
@@ -240,6 +244,9 @@ Animation::SetTimelineNoUpdate(AnimationTimeline* aTimeline)
     mHoldTime.SetNull();
   }
 
+  if (!aTimeline) {
+    MaybeQueueCancelEvent(activeTime);
+  }
   UpdateTiming(SeekFlag::NoSeek, SyncNotifyFlag::Async);
 }
 
@@ -771,6 +778,10 @@ Animation::CancelNoUpdate()
 
   DispatchPlaybackEvent(NS_LITERAL_STRING("cancel"));
 
+  StickyTimeDuration activeTime = mEffect
+                                  ? mEffect->GetComputedTiming().mActiveTime
+                                  : StickyTimeDuration();
+
   mHoldTime.SetNull();
   mStartTime.SetNull();
 
@@ -779,6 +790,7 @@ Animation::CancelNoUpdate()
   if (mTimeline) {
     mTimeline->RemoveAnimation(this);
   }
+  MaybeQueueCancelEvent(activeTime);
 }
 
 void
@@ -819,6 +831,17 @@ Animation::HasLowerCompositeOrderThan(const Animation& aOther) const
       return thisTransition->HasLowerCompositeOrderThan(*otherTransition);
     }
     if (thisTransition || otherTransition) {
+      // Cancelled transitions no longer have an owning element. To be strictly
+      // correct we should store a strong reference to the owning element
+      // so that if we arrive here while sorting cancel events, we can sort
+      // them in the correct order.
+      //
+      // However, given that cancel events are almost always queued
+      // synchronously in some deterministic manner, we can be fairly sure
+      // that cancel events will be dispatched in a deterministic order
+      // (which is our only hard requirement until specs say otherwise).
+      // Furthermore, we only reach here when we have events with equal
+      // timestamps so this is an edge case we can probably ignore for now.
       return thisTransition;
     }
   }
diff --git a/dom/animation/Animation.h b/dom/animation/Animation.h
index c59d7d6ce0..3263b30c44 100644
--- a/dom/animation/Animation.h
+++ b/dom/animation/Animation.h
@@ -326,6 +326,16 @@ public:
 
   void NotifyEffectTimingUpdated();
 
+  /**
+   * Used by subclasses to synchronously queue a cancel event in situations
+   * where the Animation may have been cancelled.
+   *
+   * We need to do this synchronously because after a CSS animation/transition
+   * is canceled, it will be released by its owning element and may not still
+   * exist when we would normally go to queue events on the next tick.
+   */
+  virtual void MaybeQueueCancelEvent(StickyTimeDuration aActiveTime) {};
+
 protected:
   void SilentlySetCurrentTime(const TimeDuration& aNewCurrentTime);
   void SilentlySetPlaybackRate(double aPlaybackRate);
diff --git a/layout/style/nsTransitionManager.cpp b/layout/style/nsTransitionManager.cpp
index 4a5ecdef6d..da12a0ecdb 100644
--- a/layout/style/nsTransitionManager.cpp
+++ b/layout/style/nsTransitionManager.cpp
@@ -180,7 +180,7 @@ CSSTransition::UpdateTiming(SeekFlag aSeekFlag, SyncNotifyFlag aSyncNotifyFlag)
 }
 
 void
-CSSTransition::QueueEvents()
+CSSTransition::QueueEvents(StickyTimeDuration aActiveTime)
 {
   if (!mEffect ||
       !mOwningElement.IsSet()) {
@@ -230,12 +230,9 @@ CSSTransition::QueueEvents()
   // Handle cancel events firts
   if (mPreviousTransitionPhase != TransitionPhase::Idle &&
       currentPhase == TransitionPhase::Idle) {
-    // FIXME: bug 1264125: We will need to get active time when cancelling
-    //                     the transition.
-    StickyTimeDuration activeTime(0);
-    TimeStamp activeTimeStamp = ElapsedTimeToTimeStamp(activeTime);
+    TimeStamp activeTimeStamp = ElapsedTimeToTimeStamp(aActiveTime);
     events.AppendElement(TransitionEventParams{ eTransitionCancel,
-                                                activeTime,
+                                                aActiveTime,
                                                 activeTimeStamp });
   }
 
diff --git a/layout/style/nsTransitionManager.h b/layout/style/nsTransitionManager.h
index 56ec61572b..80042adcdf 100644
--- a/layout/style/nsTransitionManager.h
+++ b/layout/style/nsTransitionManager.h
@@ -162,6 +162,18 @@ public:
 
     Animation::CancelFromStyle();
 
+    // The above call to Animation::CancelFromStyle may cause a transitioncancel
+    // event to be queued. However, it will also remove the transition from its
+    // timeline. If this transition was the last animation attached to
+    // the timeline, the timeline will stop observing the refresh driver and
+    // there may be no subsequent tick fro dispatching animation events.
+    //
+    // To ensure the cancel event is dispatched we tell the timeline it needs to
+    // observe the refresh driver for at least one more tick.
+    if (mTimeline) {
+      mTimeline->NotifyAnimationUpdated(*this);
+    }
+
     // It is important we do this *after* calling CancelFromStyle().
     // This is because CancelFromStyle() will end up posting a restyle and
     // that restyle should target the *transitions* level of the cascade.
@@ -214,6 +226,10 @@ public:
       const TimeDuration& aStartTime,
       double aPlaybackRate);
 
+  void MaybeQueueCancelEvent(StickyTimeDuration aActiveTime) override {
+    QueueEvents(aActiveTime);
+  }
+
 protected:
   virtual ~CSSTransition()
   {
@@ -225,7 +241,7 @@ protected:
   void UpdateTiming(SeekFlag aSeekFlag,
                     SyncNotifyFlag aSyncNotifyFlag) override;
 
-  void QueueEvents();
+  void QueueEvents(StickyTimeDuration activeTime = StickyTimeDuration());
 
   // The (pseudo-)element whose computed transition-property refers to this
   // transition (if any).