5 files changed, 19 insertions, 4 deletions
diff --git a/dom/animation/Animation.cpp b/dom/animation/Animation.cpp
index 242a0c6d6..bd318f79e 100644
--- a/dom/animation/Animation.cpp
+++ b/dom/animation/Animation.cpp
@@ -787,12 +787,21 @@ Animation::CancelNoUpdate()
   mHoldTime.SetNull();
   mStartTime.SetNull();
 
-  UpdateTiming(SeekFlag::NoSeek, SyncNotifyFlag::Async);
-
   if (mTimeline) {
     mTimeline->RemoveAnimation(this);
   }
   MaybeQueueCancelEvent(activeTime);
+
+  // When an animation is cancelled it no longer needs further ticks from the
+  // timeline. However, if we queued a cancel event and this was the last
+  // animation attached to the timeline, the timeline will stop observing the
+  // refresh driver and there may be no subsequent refresh driver tick for
+  // dispatching the queued event.
+  //
+  // By calling UpdateTiming *after* removing ourselves from our timeline, we
+  // ensure the timeline will register with the refresh driver for at least one
+  // more tick.
+  UpdateTiming(SeekFlag::NoSeek, SyncNotifyFlag::Async);
 }
 
 void
diff --git a/dom/animation/ComputedTiming.h b/dom/animation/ComputedTiming.h
index addf15865..525d59d23 100644
--- a/dom/animation/ComputedTiming.h
+++ b/dom/animation/ComputedTiming.h
@@ -64,12 +64,12 @@ struct ComputedTiming
   }
 
   enum class AnimationPhase {
-    Null,   // Not sampled (null sample time)
+    Idle,   // Not sampled (null sample time)
     Before, // Sampled prior to the start of the active interval
     Active, // Sampled within the active interval
     After   // Sampled after (or at) the end of the active interval
   };
-  AnimationPhase      mPhase = AnimationPhase::Null;
+  AnimationPhase      mPhase = AnimationPhase::Idle;
 
   ComputedTimingFunction::BeforeFlag mBeforeFlag =
     ComputedTimingFunction::BeforeFlag::Unset;
diff --git a/dom/base/nsGkAtomList.h b/dom/base/nsGkAtomList.h
index 09d73e617..948487083 100644
--- a/dom/base/nsGkAtomList.h
+++ b/dom/base/nsGkAtomList.h
@@ -694,6 +694,7 @@ GK_ATOM(onadapterremoved, "onadapterremoved")
 GK_ATOM(onafterprint, "onafterprint")
 GK_ATOM(onafterscriptexecute, "onafterscriptexecute")
 GK_ATOM(onalerting, "onalerting")
+GK_ATOM(onanimationcancel, "onanimationcancel")
 GK_ATOM(onanimationend, "onanimationend")
 GK_ATOM(onanimationiteration, "onanimationiteration")
 GK_ATOM(onanimationstart, "onanimationstart")
diff --git a/dom/events/EventNameList.h b/dom/events/EventNameList.h
index 61942b251..00478c87b 100644
--- a/dom/events/EventNameList.h
+++ b/dom/events/EventNameList.h
@@ -1019,6 +1019,10 @@ EVENT(animationiteration,
       eAnimationIteration,
       EventNameType_All,
       eAnimationEventClass)
+EVENT(animationcancel,
+      eAnimationCancel,
+      EventNameType_All,
+      eAnimationEventClass)
 
 // Webkit-prefixed versions of Transition & Animation events, for web compat:
 EVENT(webkitAnimationEnd,
diff --git a/dom/webidl/EventHandler.webidl b/dom/webidl/EventHandler.webidl
index 6691ca224..306372ff1 100644
--- a/dom/webidl/EventHandler.webidl
+++ b/dom/webidl/EventHandler.webidl
@@ -128,6 +128,7 @@ interface GlobalEventHandlers {
            attribute EventHandler onmozpointerlockerror;
 
            // CSS-Animation and CSS-Transition handlers.
+           attribute EventHandler onanimationcancel;
            attribute EventHandler onanimationend;
            attribute EventHandler onanimationiteration;
            attribute EventHandler onanimationstart;