Bug 1799064 - Avoid potential call PostUpdate() twice in SetTimeline(). r=emilio

Basically, in SetTimelineNoUpdate(), we shouldn't call PostUpdate(). So we
shouldn't call SetCurrentTime() directly.

There is no behavior change. Just make sure we don't PostUpdate twice
while updating an existing CSS animation via changing animation-timeline.

Differential Revision: https://phabricator.services.mozilla.com/D161245

dom/animation/Animation.cpp

@@ -308,7 +308,8 @@ void Animation::SetTimelineNoUpdate(AnimationTimeline* aTimeline) {
   } else if (oldTimeline && !oldTimeline->IsMonotonicallyIncreasing() &&
              !previousCurrentTime.IsNull()) {
     // If "from finite timeline" and previous progress is resolved.
-    SetCurrentTime(TimeDuration(EffectEnd().MultDouble(previousProgress)));
+    SetCurrentTimeNoUpdate(
+        TimeDuration(EffectEnd().MultDouble(previousProgress)));
   }
 
   if (!mStartTime.IsNull()) {
@@ -322,6 +323,9 @@ void Animation::SetTimelineNoUpdate(AnimationTimeline* aTimeline) {
   UpdatePendingAnimationTracker(oldTimeline, aTimeline);
 
   UpdateTiming(SeekFlag::NoSeek, SyncNotifyFlag::Async);
+
+  // FIXME: Bug 1799071: Check if we need to add
+  // MutationObservers::NotifyAnimationChanged(this) here.
 }
 
 // https://drafts.csswg.org/web-animations/#set-the-animation-start-time
@@ -408,6 +412,15 @@ void Animation::SetCurrentTime(const TimeDuration& aSeekTime) {
 
   AutoMutationBatchForAnimation mb(*this);
 
+  SetCurrentTimeNoUpdate(aSeekTime);
+
+  if (IsRelevant()) {
+    MutationObservers::NotifyAnimationChanged(this);
+  }
+  PostUpdate();
+}
+
+void Animation::SetCurrentTimeNoUpdate(const TimeDuration& aSeekTime) {
   SilentlySetCurrentTime(aSeekTime);
 
   if (mPendingState == PendingState::PausePending) {
@@ -424,10 +437,6 @@ void Animation::SetCurrentTime(const TimeDuration& aSeekTime) {
   }
 
   UpdateTiming(SeekFlag::DidSeek, SyncNotifyFlag::Async);
-  if (IsRelevant()) {
-    MutationObservers::NotifyAnimationChanged(this);
-  }
-  PostUpdate();
 }
 
 // https://drafts.csswg.org/web-animations/#set-the-playback-rate

dom/animation/Animation.h

@@ -111,7 +111,8 @@ class Animation : public DOMEventTargetHelper,
     return GetCurrentTimeForHoldTime(mHoldTime);
   }
   Nullable<double> GetCurrentTimeAsDouble() const;
-  void SetCurrentTime(const TimeDuration& aNewCurrentTime);
+  void SetCurrentTime(const TimeDuration& aSeekTime);
+  void SetCurrentTimeNoUpdate(const TimeDuration& aSeekTime);
   void SetCurrentTimeAsDouble(const Nullable<double>& aCurrentTime,
                               ErrorResult& aRv);