Adding upstream version 124.0.1.upstream/124.0.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1992 insertions, 0 deletions

diff --git a/dom/animation/Animation.cpp b/dom/animation/Animation.cpp
new file mode 100644
index 0000000000..6f0fee007c
--- /dev/null
+++ b/dom/animation/Animation.cpp
@@ -0,0 +1,1992 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "Animation.h"
+
+#include "nsIFrame.h"
+#include "AnimationUtils.h"
+#include "mozAutoDocUpdate.h"
+#include "mozilla/dom/AnimationBinding.h"
+#include "mozilla/dom/AnimationPlaybackEvent.h"
+#include "mozilla/dom/Document.h"
+#include "mozilla/dom/DocumentInlines.h"
+#include "mozilla/dom/DocumentTimeline.h"
+#include "mozilla/dom/MutationObservers.h"
+#include "mozilla/dom/Promise.h"
+#include "mozilla/AnimationEventDispatcher.h"
+#include "mozilla/AnimationTarget.h"
+#include "mozilla/AutoRestore.h"
+#include "mozilla/CycleCollectedJSContext.h"
+#include "mozilla/DeclarationBlock.h"
+#include "mozilla/Maybe.h"  // For Maybe
+#include "mozilla/StaticPrefs_dom.h"
+#include "nsAnimationManager.h"  // For CSSAnimation
+#include "nsComputedDOMStyle.h"
+#include "nsDOMMutationObserver.h"    // For nsAutoAnimationMutationBatch
+#include "nsDOMCSSAttrDeclaration.h"  // For nsDOMCSSAttributeDeclaration
+#include "nsThreadUtils.h"  // For nsRunnableMethod and nsRevocableEventPtr
+#include "nsTransitionManager.h"  // For CSSTransition
+#include "ScrollTimelineAnimationTracker.h"
+
+namespace mozilla::dom {
+
+// Static members
+uint64_t Animation::sNextAnimationIndex = 0;
+
+NS_IMPL_CYCLE_COLLECTION_INHERITED(Animation, DOMEventTargetHelper, mTimeline,
+                                   mEffect, mReady, mFinished)
+
+NS_IMPL_ADDREF_INHERITED(Animation, DOMEventTargetHelper)
+NS_IMPL_RELEASE_INHERITED(Animation, DOMEventTargetHelper)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(Animation)
+NS_INTERFACE_MAP_END_INHERITING(DOMEventTargetHelper)
+
+JSObject* Animation::WrapObject(JSContext* aCx,
+                                JS::Handle<JSObject*> aGivenProto) {
+  return dom::Animation_Binding::Wrap(aCx, this, aGivenProto);
+}
+
+// ---------------------------------------------------------------------------
+//
+// Utility methods
+//
+// ---------------------------------------------------------------------------
+
+namespace {
+// A wrapper around nsAutoAnimationMutationBatch that looks up the
+// appropriate document from the supplied animation.
+class MOZ_RAII AutoMutationBatchForAnimation {
+ public:
+  explicit AutoMutationBatchForAnimation(const Animation& aAnimation) {
+    NonOwningAnimationTarget target = aAnimation.GetTargetForAnimation();
+    if (!target) {
+      return;
+    }
+
+    // For mutation observers, we use the OwnerDoc.
+    mAutoBatch.emplace(target.mElement->OwnerDoc());
+  }
+
+ private:
+  Maybe<nsAutoAnimationMutationBatch> mAutoBatch;
+};
+}  // namespace
+
+// ---------------------------------------------------------------------------
+//
+// Animation interface:
+//
+// ---------------------------------------------------------------------------
+
+Animation::Animation(nsIGlobalObject* aGlobal)
+    : DOMEventTargetHelper(aGlobal),
+      mAnimationIndex(sNextAnimationIndex++),
+      mRTPCallerType(aGlobal->GetRTPCallerType()) {}
+
+Animation::~Animation() = default;
+
+/* static */
+already_AddRefed<Animation> Animation::ClonePausedAnimation(
+    nsIGlobalObject* aGlobal, const Animation& aOther, AnimationEffect& aEffect,
+    AnimationTimeline& aTimeline) {
+  // FIXME: Bug 1805950: Support printing for scroll-timeline once we resolve
+  // the spec issue.
+  if (aOther.UsingScrollTimeline()) {
+    return nullptr;
+  }
+
+  RefPtr<Animation> animation = new Animation(aGlobal);
+
+  // Setup the timeline. We always use document-timeline of the new document,
+  // even if the timeline of |aOther| is null.
+  animation->mTimeline = &aTimeline;
+
+  // Setup the playback rate.
+  animation->mPlaybackRate = aOther.mPlaybackRate;
+
+  // Setup the timing.
+  const Nullable<TimeDuration> currentTime = aOther.GetCurrentTimeAsDuration();
+  if (!aOther.GetTimeline()) {
+    // This simulates what we do in SetTimelineNoUpdate(). It's possible to
+    // preserve the progress if the previous timeline is a scroll-timeline.
+    // So for null timeline, it may have a progress and the non-null current
+    // time.
+    if (!currentTime.IsNull()) {
+      animation->SilentlySetCurrentTime(currentTime.Value());
+    }
+    animation->mPreviousCurrentTime = animation->GetCurrentTimeAsDuration();
+  } else {
+    animation->mHoldTime = currentTime;
+    if (!currentTime.IsNull()) {
+      // FIXME: Should we use |timelineTime| as previous current time here? It
+      // seems we should use animation->GetCurrentTimeAsDuration(), per
+      // UpdateFinishedState().
+      const Nullable<TimeDuration> timelineTime =
+          aTimeline.GetCurrentTimeAsDuration();
+      MOZ_ASSERT(!timelineTime.IsNull(), "Timeline not yet set");
+      animation->mPreviousCurrentTime = timelineTime;
+    }
+  }
+
+  // Setup the effect's link to this.
+  animation->mEffect = &aEffect;
+  animation->mEffect->SetAnimation(animation);
+
+  animation->mPendingState = PendingState::PausePending;
+
+  // We expect our relevance to be the same as the orginal.
+  animation->mIsRelevant = aOther.mIsRelevant;
+
+  animation->PostUpdate();
+  animation->mTimeline->NotifyAnimationUpdated(*animation);
+  return animation.forget();
+}
+
+NonOwningAnimationTarget Animation::GetTargetForAnimation() const {
+  AnimationEffect* effect = GetEffect();
+  NonOwningAnimationTarget target;
+  if (!effect || !effect->AsKeyframeEffect()) {
+    return target;
+  }
+  return effect->AsKeyframeEffect()->GetAnimationTarget();
+}
+
+/* static */
+already_AddRefed<Animation> Animation::Constructor(
+    const GlobalObject& aGlobal, AnimationEffect* aEffect,
+    const Optional<AnimationTimeline*>& aTimeline, ErrorResult& aRv) {
+  nsCOMPtr<nsIGlobalObject> global = do_QueryInterface(aGlobal.GetAsSupports());
+
+  AnimationTimeline* timeline;
+  Document* document =
+      AnimationUtils::GetCurrentRealmDocument(aGlobal.Context());
+
+  if (aTimeline.WasPassed()) {
+    timeline = aTimeline.Value();
+  } else {
+    if (!document) {
+      aRv.Throw(NS_ERROR_FAILURE);
+      return nullptr;
+    }
+    timeline = document->Timeline();
+  }
+
+  RefPtr<Animation> animation = new Animation(global);
+  animation->SetTimelineNoUpdate(timeline);
+  animation->SetEffectNoUpdate(aEffect);
+
+  return animation.forget();
+}
+
+void Animation::SetId(const nsAString& aId) {
+  if (mId == aId) {
+    return;
+  }
+  mId = aId;
+  MutationObservers::NotifyAnimationChanged(this);
+}
+
+void Animation::SetEffect(AnimationEffect* aEffect) {
+  SetEffectNoUpdate(aEffect);
+  PostUpdate();
+}
+
+// https://drafts.csswg.org/web-animations/#setting-the-target-effect
+void Animation::SetEffectNoUpdate(AnimationEffect* aEffect) {
+  RefPtr<Animation> kungFuDeathGrip(this);
+
+  if (mEffect == aEffect) {
+    return;
+  }
+
+  AutoMutationBatchForAnimation mb(*this);
+  bool wasRelevant = mIsRelevant;
+
+  if (mEffect) {
+    // We need to notify observers now because once we set mEffect to null
+    // we won't be able to find the target element to notify.
+    if (mIsRelevant) {
+      MutationObservers::NotifyAnimationRemoved(this);
+    }
+
+    // Break links with the old effect and then drop it.
+    RefPtr<AnimationEffect> oldEffect = mEffect;
+    mEffect = nullptr;
+    if (IsPartialPrerendered()) {
+      if (KeyframeEffect* oldKeyframeEffect = oldEffect->AsKeyframeEffect()) {
+        oldKeyframeEffect->ResetPartialPrerendered();
+      }
+    }
+    oldEffect->SetAnimation(nullptr);
+
+    // The following will not do any notification because mEffect is null.
+    UpdateRelevance();
+  }
+
+  if (aEffect) {
+    // Break links from the new effect to its previous animation, if any.
+    RefPtr<AnimationEffect> newEffect = aEffect;
+    Animation* prevAnim = aEffect->GetAnimation();
+    if (prevAnim) {
+      prevAnim->SetEffect(nullptr);
+    }
+
+    // Create links with the new effect. SetAnimation(this) will also update
+    // mIsRelevant of this animation, and then notify mutation observer if
+    // needed by calling Animation::UpdateRelevance(), so we don't need to
+    // call it again.
+    mEffect = newEffect;
+    mEffect->SetAnimation(this);
+
+    // Notify possible add or change.
+    // If the target is different, the change notification will be ignored by
+    // AutoMutationBatchForAnimation.
+    if (wasRelevant && mIsRelevant) {
+      MutationObservers::NotifyAnimationChanged(this);
+    }
+  }
+
+  MaybeScheduleReplacementCheck();
+
+  UpdateTiming(SeekFlag::NoSeek, SyncNotifyFlag::Async);
+}
+
+void Animation::SetTimeline(AnimationTimeline* aTimeline) {
+  SetTimelineNoUpdate(aTimeline);
+  PostUpdate();
+}
+
+// https://drafts.csswg.org/web-animations/#setting-the-timeline
+void Animation::SetTimelineNoUpdate(AnimationTimeline* aTimeline) {
+  if (mTimeline == aTimeline) {
+    return;
+  }
+
+  StickyTimeDuration activeTime =
+      mEffect ? mEffect->GetComputedTiming().mActiveTime : StickyTimeDuration();
+
+  const AnimationPlayState previousPlayState = PlayState();
+  const Nullable<TimeDuration> previousCurrentTime = GetCurrentTimeAsDuration();
+  // FIXME: The definition of end time in web-animation-1 is different from that
+  // in web-animation-2, which includes the start time. We are still using the
+  // definition in web-animation-1 here for now.
+  const TimeDuration endTime = TimeDuration(EffectEnd());
+  double previousProgress = 0.0;
+  if (!previousCurrentTime.IsNull() && !endTime.IsZero()) {
+    previousProgress =
+        previousCurrentTime.Value().ToSeconds() / endTime.ToSeconds();
+  }
+
+  RefPtr<AnimationTimeline> oldTimeline = mTimeline;
+  if (oldTimeline) {
+    oldTimeline->RemoveAnimation(this);
+  }
+
+  mTimeline = aTimeline;
+
+  mResetCurrentTimeOnResume = false;
+
+  if (mEffect) {
+    mEffect->UpdateNormalizedTiming();
+  }
+
+  if (mTimeline && !mTimeline->IsMonotonicallyIncreasing()) {
+    // If "to finite timeline" is true.
+
+    ApplyPendingPlaybackRate();
+    Nullable<TimeDuration> seekTime;
+    if (mPlaybackRate >= 0.0) {
+      seekTime.SetValue(TimeDuration());
+    } else {
+      seekTime.SetValue(TimeDuration(EffectEnd()));
+    }
+
+    switch (previousPlayState) {
+      case AnimationPlayState::Running:
+      case AnimationPlayState::Finished:
+        mStartTime = seekTime;
+        break;
+      case AnimationPlayState::Paused:
+        if (!previousCurrentTime.IsNull()) {
+          mResetCurrentTimeOnResume = true;
+          mStartTime.SetNull();
+          mHoldTime.SetValue(
+              TimeDuration(EffectEnd().MultDouble(previousProgress)));
+        } else {
+          mStartTime = seekTime;
+        }
+        break;
+      case AnimationPlayState::Idle:
+      default:
+        break;
+    }
+  } else if (oldTimeline && !oldTimeline->IsMonotonicallyIncreasing() &&
+             !previousCurrentTime.IsNull()) {
+    // If "from finite timeline" and previous progress is resolved.
+    SetCurrentTimeNoUpdate(
+        TimeDuration(EffectEnd().MultDouble(previousProgress)));
+  }
+
+  if (!mStartTime.IsNull()) {
+    mHoldTime.SetNull();
+  }
+
+  if (!aTimeline) {
+    MaybeQueueCancelEvent(activeTime);
+  }
+
+  UpdateScrollTimelineAnimationTracker(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
+void Animation::SetStartTime(const Nullable<TimeDuration>& aNewStartTime) {
+  // Return early if the start time will not change. However, if we
+  // are pending, then setting the start time to any value
+  // including the current value has the effect of aborting
+  // pending tasks so we should not return early in that case.
+  if (!Pending() && aNewStartTime == mStartTime) {
+    return;
+  }
+
+  AutoMutationBatchForAnimation mb(*this);
+
+  Nullable<TimeDuration> timelineTime;
+  if (mTimeline) {
+    // The spec says to check if the timeline is active (has a resolved time)
+    // before using it here, but we don't need to since it's harmless to set
+    // the already null time to null.
+    timelineTime = mTimeline->GetCurrentTimeAsDuration();
+  }
+  if (timelineTime.IsNull() && !aNewStartTime.IsNull()) {
+    mHoldTime.SetNull();
+  }
+
+  Nullable<TimeDuration> previousCurrentTime = GetCurrentTimeAsDuration();
+
+  ApplyPendingPlaybackRate();
+  mStartTime = aNewStartTime;
+
+  mResetCurrentTimeOnResume = false;
+
+  if (!aNewStartTime.IsNull()) {
+    if (mPlaybackRate != 0.0) {
+      mHoldTime.SetNull();
+    }
+  } else {
+    mHoldTime = previousCurrentTime;
+  }
+
+  CancelPendingTasks();
+  if (mReady) {
+    // We may have already resolved mReady, but in that case calling
+    // MaybeResolve is a no-op, so that's okay.
+    mReady->MaybeResolve(this);
+  }
+
+  UpdateTiming(SeekFlag::DidSeek, SyncNotifyFlag::Async);
+  if (IsRelevant()) {
+    MutationObservers::NotifyAnimationChanged(this);
+  }
+  PostUpdate();
+}
+
+// https://drafts.csswg.org/web-animations/#current-time
+Nullable<TimeDuration> Animation::GetCurrentTimeForHoldTime(
+    const Nullable<TimeDuration>& aHoldTime) const {
+  Nullable<TimeDuration> result;
+  if (!aHoldTime.IsNull()) {
+    result = aHoldTime;
+    return result;
+  }
+
+  if (mTimeline && !mStartTime.IsNull()) {
+    Nullable<TimeDuration> timelineTime = mTimeline->GetCurrentTimeAsDuration();
+    if (!timelineTime.IsNull()) {
+      result = CurrentTimeFromTimelineTime(timelineTime.Value(),
+                                           mStartTime.Value(), mPlaybackRate);
+    }
+  }
+  return result;
+}
+
+// https://drafts.csswg.org/web-animations/#set-the-current-time
+void Animation::SetCurrentTime(const TimeDuration& aSeekTime) {
+  // Return early if the current time has not changed. However, if we
+  // are pause-pending, then setting the current time to any value
+  // including the current value has the effect of aborting the
+  // pause so we should not return early in that case.
+  if (mPendingState != PendingState::PausePending &&
+      Nullable<TimeDuration>(aSeekTime) == GetCurrentTimeAsDuration()) {
+    return;
+  }
+
+  AutoMutationBatchForAnimation mb(*this);
+
+  SetCurrentTimeNoUpdate(aSeekTime);
+
+  if (IsRelevant()) {
+    MutationObservers::NotifyAnimationChanged(this);
+  }
+  PostUpdate();
+}
+
+void Animation::SetCurrentTimeNoUpdate(const TimeDuration& aSeekTime) {
+  SilentlySetCurrentTime(aSeekTime);
+
+  if (mPendingState == PendingState::PausePending) {
+    // Finish the pause operation
+    mHoldTime.SetValue(aSeekTime);
+
+    ApplyPendingPlaybackRate();
+    mStartTime.SetNull();
+
+    if (mReady) {
+      mReady->MaybeResolve(this);
+    }
+    CancelPendingTasks();
+  }
+
+  UpdateTiming(SeekFlag::DidSeek, SyncNotifyFlag::Async);
+}
+
+// https://drafts.csswg.org/web-animations/#set-the-playback-rate
+void Animation::SetPlaybackRate(double aPlaybackRate) {
+  mPendingPlaybackRate.reset();
+
+  if (aPlaybackRate == mPlaybackRate) {
+    return;
+  }
+
+  AutoMutationBatchForAnimation mb(*this);
+
+  Nullable<TimeDuration> previousTime = GetCurrentTimeAsDuration();
+  mPlaybackRate = aPlaybackRate;
+  if (!previousTime.IsNull()) {
+    SetCurrentTime(previousTime.Value());
+  }
+
+  // In the case where GetCurrentTimeAsDuration() returns the same result before
+  // and after updating mPlaybackRate, SetCurrentTime will return early since,
+  // as far as it can tell, nothing has changed.
+  // As a result, we need to perform the following updates here:
+  // - update timing (since, if the sign of the playback rate has changed, our
+  //   finished state may have changed),
+  // - dispatch a change notification for the changed playback rate, and
+  // - update the playback rate on animations on layers.
+  UpdateTiming(SeekFlag::DidSeek, SyncNotifyFlag::Async);
+  if (IsRelevant()) {
+    MutationObservers::NotifyAnimationChanged(this);
+  }
+  PostUpdate();
+}
+
+// https://drafts.csswg.org/web-animations/#seamlessly-update-the-playback-rate
+void Animation::UpdatePlaybackRate(double aPlaybackRate) {
+  if (mPendingPlaybackRate && mPendingPlaybackRate.value() == aPlaybackRate) {
+    return;
+  }
+
+  // Calculate the play state using the existing playback rate since below we
+  // want to know if the animation is _currently_ finished or not, not whether
+  // it _will_ be finished.
+  AnimationPlayState playState = PlayState();
+
+  mPendingPlaybackRate = Some(aPlaybackRate);
+
+  if (Pending()) {
+    // If we already have a pending task, there is nothing more to do since the
+    // playback rate will be applied then.
+    //
+    // However, as with the idle/paused case below, we still need to update the
+    // relevance (and effect set to make sure it only contains relevant
+    // animations) since the relevance is based on the Animation play state
+    // which incorporates the _pending_ playback rate.
+    UpdateEffect(PostRestyleMode::Never);
+    return;
+  }
+
+  AutoMutationBatchForAnimation mb(*this);
+
+  if (playState == AnimationPlayState::Idle ||
+      playState == AnimationPlayState::Paused ||
+      GetCurrentTimeAsDuration().IsNull()) {
+    // If |previous play state| is idle or paused, or the current time is
+    // unresolved, we apply any pending playback rate on animation immediately.
+    ApplyPendingPlaybackRate();
+
+    // We don't need to update timing or post an update here because:
+    //
+    // * the current time hasn't changed -- it's either unresolved or fixed
+    //   with a hold time -- so the output won't have changed
+    // * the finished state won't have changed even if the sign of the
+    //   playback rate changed since we're not finished (we're paused or idle)
+    // * the playback rate on layers doesn't need to be updated since we're not
+    //   moving. Once we get a start time etc. we'll update the playback rate
+    //   then.
+    //
+    // However we still need to update the relevance and effect set as well as
+    // notifying observers.
+    UpdateEffect(PostRestyleMode::Never);
+    if (IsRelevant()) {
+      MutationObservers::NotifyAnimationChanged(this);
+    }
+  } else if (playState == AnimationPlayState::Finished) {
+    MOZ_ASSERT(mTimeline && !mTimeline->GetCurrentTimeAsDuration().IsNull(),
+               "If we have no active timeline, we should be idle or paused");
+    if (aPlaybackRate != 0) {
+      // The unconstrained current time can only be unresolved if either we
+      // don't have an active timeline (and we already asserted that is not
+      // true) or we have an unresolved start time (in which case we should be
+      // paused).
+      MOZ_ASSERT(!GetUnconstrainedCurrentTime().IsNull(),
+                 "Unconstrained current time should be resolved");
+      TimeDuration unconstrainedCurrentTime =
+          GetUnconstrainedCurrentTime().Value();
+      TimeDuration timelineTime = mTimeline->GetCurrentTimeAsDuration().Value();
+      mStartTime = StartTimeFromTimelineTime(
+          timelineTime, unconstrainedCurrentTime, aPlaybackRate);
+    } else {
+      mStartTime = mTimeline->GetCurrentTimeAsDuration();
+    }
+
+    ApplyPendingPlaybackRate();
+
+    // Even though we preserve the current time, we might now leave the finished
+    // state (e.g. if the playback rate changes sign) so we need to update
+    // timing.
+    UpdateTiming(SeekFlag::NoSeek, SyncNotifyFlag::Async);
+    if (IsRelevant()) {
+      MutationObservers::NotifyAnimationChanged(this);
+    }
+    PostUpdate();
+  } else {
+    ErrorResult rv;
+    Play(rv, LimitBehavior::Continue);
+    MOZ_ASSERT(!rv.Failed(),
+               "We should only fail to play when using auto-rewind behavior");
+  }
+}
+
+// https://drafts.csswg.org/web-animations/#play-state
+AnimationPlayState Animation::PlayState() const {
+  Nullable<TimeDuration> currentTime = GetCurrentTimeAsDuration();
+  if (currentTime.IsNull() && mStartTime.IsNull() && !Pending()) {
+    return AnimationPlayState::Idle;
+  }
+
+  if (mPendingState == PendingState::PausePending ||
+      (mStartTime.IsNull() && !Pending())) {
+    return AnimationPlayState::Paused;
+  }
+
+  double playbackRate = CurrentOrPendingPlaybackRate();
+  if (!currentTime.IsNull() &&
+      ((playbackRate > 0.0 && currentTime.Value() >= EffectEnd()) ||
+       (playbackRate < 0.0 && currentTime.Value() <= TimeDuration()))) {
+    return AnimationPlayState::Finished;
+  }
+
+  return AnimationPlayState::Running;
+}
+
+Promise* Animation::GetReady(ErrorResult& aRv) {
+  nsCOMPtr<nsIGlobalObject> global = GetOwnerGlobal();
+  if (!mReady && global) {
+    mReady = Promise::Create(global, aRv);  // Lazily create on demand
+  }
+  if (!mReady) {
+    aRv.Throw(NS_ERROR_FAILURE);
+    return nullptr;
+  }
+  if (!Pending()) {
+    mReady->MaybeResolve(this);
+  }
+  return mReady;
+}
+
+Promise* Animation::GetFinished(ErrorResult& aRv) {
+  nsCOMPtr<nsIGlobalObject> global = GetOwnerGlobal();
+  if (!mFinished && global) {
+    mFinished = Promise::Create(global, aRv);  // Lazily create on demand
+  }
+  if (!mFinished) {
+    aRv.Throw(NS_ERROR_FAILURE);
+    return nullptr;
+  }
+  if (mFinishedIsResolved) {
+    MaybeResolveFinishedPromise();
+  }
+  return mFinished;
+}
+
+// https://drafts.csswg.org/web-animations/#cancel-an-animation
+void Animation::Cancel(PostRestyleMode aPostRestyle) {
+  bool newlyIdle = false;
+
+  if (PlayState() != AnimationPlayState::Idle) {
+    newlyIdle = true;
+
+    ResetPendingTasks();
+
+    if (mFinished) {
+      mFinished->MaybeReject(NS_ERROR_DOM_ABORT_ERR);
+      // mFinished can already be resolved.
+      MOZ_ALWAYS_TRUE(mFinished->SetAnyPromiseIsHandled());
+    }
+    ResetFinishedPromise();
+
+    QueuePlaybackEvent(u"cancel"_ns, GetTimelineCurrentTimeAsTimeStamp());
+  }
+
+  StickyTimeDuration activeTime =
+      mEffect ? mEffect->GetComputedTiming().mActiveTime : StickyTimeDuration();
+
+  mHoldTime.SetNull();
+  mStartTime.SetNull();
+
+  // Allow our effect to remove itself from the its target element's EffectSet.
+  UpdateEffect(aPostRestyle);
+
+  if (mTimeline) {
+    mTimeline->RemoveAnimation(this);
+  }
+  MaybeQueueCancelEvent(activeTime);
+
+  if (newlyIdle && aPostRestyle == PostRestyleMode::IfNeeded) {
+    PostUpdate();
+  }
+}
+
+// https://drafts.csswg.org/web-animations/#finish-an-animation
+void Animation::Finish(ErrorResult& aRv) {
+  double effectivePlaybackRate = CurrentOrPendingPlaybackRate();
+
+  if (effectivePlaybackRate == 0) {
+    return aRv.ThrowInvalidStateError(
+        "Can't finish animation with zero playback rate");
+  }
+  if (effectivePlaybackRate > 0 && EffectEnd() == TimeDuration::Forever()) {
+    return aRv.ThrowInvalidStateError("Can't finish infinite animation");
+  }
+
+  AutoMutationBatchForAnimation mb(*this);
+
+  ApplyPendingPlaybackRate();
+
+  // Seek to the end
+  TimeDuration limit =
+      mPlaybackRate > 0 ? TimeDuration(EffectEnd()) : TimeDuration(0);
+  bool didChange = GetCurrentTimeAsDuration() != Nullable<TimeDuration>(limit);
+  SilentlySetCurrentTime(limit);
+
+  // If we are paused or play-pending we need to fill in the start time in
+  // order to transition to the finished state.
+  //
+  // We only do this, however, if we have an active timeline. If we have an
+  // inactive timeline we can't transition into the finished state just like
+  // we can't transition to the running state (this finished state is really
+  // a substate of the running state).
+  if (mStartTime.IsNull() && mTimeline &&
+      !mTimeline->GetCurrentTimeAsDuration().IsNull()) {
+    mStartTime = StartTimeFromTimelineTime(
+        mTimeline->GetCurrentTimeAsDuration().Value(), limit, mPlaybackRate);
+    didChange = true;
+  }
+
+  // If we just resolved the start time for a pause or play-pending
+  // animation, we need to clear the task. We don't do this as a branch of
+  // the above however since we can have a play-pending animation with a
+  // resolved start time if we aborted a pause operation.
+  if (!mStartTime.IsNull() && (mPendingState == PendingState::PlayPending ||
+                               mPendingState == PendingState::PausePending)) {
+    if (mPendingState == PendingState::PausePending) {
+      mHoldTime.SetNull();
+    }
+    CancelPendingTasks();
+    didChange = true;
+    if (mReady) {
+      mReady->MaybeResolve(this);
+    }
+  }
+  UpdateTiming(SeekFlag::DidSeek, SyncNotifyFlag::Sync);
+  if (didChange && IsRelevant()) {
+    MutationObservers::NotifyAnimationChanged(this);
+  }
+  PostUpdate();
+}
+
+void Animation::Play(ErrorResult& aRv, LimitBehavior aLimitBehavior) {
+  PlayNoUpdate(aRv, aLimitBehavior);
+  PostUpdate();
+}
+
+// https://drafts.csswg.org/web-animations/#reverse-an-animation
+void Animation::Reverse(ErrorResult& aRv) {
+  if (!mTimeline) {
+    return aRv.ThrowInvalidStateError(
+        "Can't reverse an animation with no associated timeline");
+  }
+  if (mTimeline->GetCurrentTimeAsDuration().IsNull()) {
+    return aRv.ThrowInvalidStateError(
+        "Can't reverse an animation associated with an inactive timeline");
+  }
+
+  double effectivePlaybackRate = CurrentOrPendingPlaybackRate();
+
+  if (effectivePlaybackRate == 0.0) {
+    return;
+  }
+
+  Maybe<double> originalPendingPlaybackRate = mPendingPlaybackRate;
+
+  mPendingPlaybackRate = Some(-effectivePlaybackRate);
+
+  Play(aRv, LimitBehavior::AutoRewind);
+
+  // If Play() threw, restore state and don't report anything to mutation
+  // observers.
+  if (aRv.Failed()) {
+    mPendingPlaybackRate = originalPendingPlaybackRate;
+  }
+
+  // Play(), above, unconditionally calls PostUpdate so we don't need to do
+  // it here.
+}
+
+void Animation::Persist() {
+  if (mReplaceState == AnimationReplaceState::Persisted) {
+    return;
+  }
+
+  bool wasRemoved = mReplaceState == AnimationReplaceState::Removed;
+
+  mReplaceState = AnimationReplaceState::Persisted;
+
+  // If the animation is not (yet) removed, there should be no side effects of
+  // persisting it.
+  if (wasRemoved) {
+    UpdateEffect(PostRestyleMode::IfNeeded);
+    PostUpdate();
+  }
+}
+
+DocGroup* Animation::GetDocGroup() {
+  Document* doc = GetRenderedDocument();
+  return doc ? doc->GetDocGroup() : nullptr;
+}
+
+// https://drafts.csswg.org/web-animations/#dom-animation-commitstyles
+void Animation::CommitStyles(ErrorResult& aRv) {
+  if (!mEffect) {
+    return;
+  }
+
+  // Take an owning reference to the keyframe effect. This will ensure that
+  // this Animation and the target element remain alive after flushing style.
+  RefPtr<KeyframeEffect> keyframeEffect = mEffect->AsKeyframeEffect();
+  if (!keyframeEffect) {
+    return;
+  }
+
+  NonOwningAnimationTarget target = keyframeEffect->GetAnimationTarget();
+  if (!target) {
+    return;
+  }
+
+  if (target.mPseudoType != PseudoStyleType::NotPseudo) {
+    return aRv.ThrowNoModificationAllowedError(
+        "Can't commit styles of a pseudo-element");
+  }
+
+  // Check it is an element with a style attribute
+  RefPtr<nsStyledElement> styledElement =
+      nsStyledElement::FromNodeOrNull(target.mElement);
+  if (!styledElement) {
+    return aRv.ThrowNoModificationAllowedError(
+        "Target is not capable of having a style attribute");
+  }
+
+  // Hold onto a strong reference to the doc in case the flush destroys it.
+  RefPtr<Document> doc = target.mElement->GetComposedDoc();
+
+  // Flush frames before checking if the target element is rendered since the
+  // result could depend on pending style changes, and IsRendered() looks at the
+  // primary frame.
+  if (doc) {
+    doc->FlushPendingNotifications(FlushType::Frames);
+  }
+  if (!target.mElement->IsRendered()) {
+    return aRv.ThrowInvalidStateError("Target is not rendered");
+  }
+  nsPresContext* presContext =
+      nsContentUtils::GetContextForContent(target.mElement);
+  if (!presContext) {
+    return aRv.ThrowInvalidStateError("Target is not rendered");
+  }
+
+  // Get the computed animation values
+  UniquePtr<StyleAnimationValueMap> animationValues(
+      Servo_AnimationValueMap_Create());
+  if (!presContext->EffectCompositor()->ComposeServoAnimationRuleForEffect(
+          *keyframeEffect, CascadeLevel(), animationValues.get())) {
+    NS_WARNING("Failed to compose animation style to commit");
+    return;
+  }
+
+  // Calling SetCSSDeclaration will trigger attribute setting code.
+  // Start the update now so that the old rule doesn't get used
+  // between when we mutate the declaration and when we set the new
+  // rule.
+  mozAutoDocUpdate autoUpdate(target.mElement->OwnerDoc(), true);
+
+  // Get the inline style to append to
+  RefPtr<DeclarationBlock> declarationBlock;
+  if (auto* existing = target.mElement->GetInlineStyleDeclaration()) {
+    declarationBlock = existing->EnsureMutable();
+  } else {
+    declarationBlock = new DeclarationBlock();
+    declarationBlock->SetDirty();
+  }
+
+  // Prepare the callback
+  MutationClosureData closureData;
+  closureData.mShouldBeCalled = true;
+  closureData.mElement = target.mElement;
+  DeclarationBlockMutationClosure beforeChangeClosure = {
+      nsDOMCSSAttributeDeclaration::MutationClosureFunction,
+      &closureData,
+  };
+
+  // Set the animated styles
+  bool changed = false;
+  const AnimatedPropertyIDSet& properties = keyframeEffect->GetPropertySet();
+  for (const AnimatedPropertyID& property : properties) {
+    RefPtr<StyleAnimationValue> computedValue =
+        Servo_AnimationValueMap_GetValue(animationValues.get(), &property)
+            .Consume();
+    if (computedValue) {
+      changed |= Servo_DeclarationBlock_SetPropertyToAnimationValue(
+          declarationBlock->Raw(), computedValue, beforeChangeClosure);
+    }
+  }
+
+  if (!changed) {
+    MOZ_ASSERT(!closureData.mWasCalled);
+    return;
+  }
+
+  MOZ_ASSERT(closureData.mWasCalled);
+  // Update inline style declaration
+  target.mElement->SetInlineStyleDeclaration(*declarationBlock, closureData);
+}
+
+// ---------------------------------------------------------------------------
+//
+// JS wrappers for Animation interface:
+//
+// ---------------------------------------------------------------------------
+
+Nullable<double> Animation::GetStartTimeAsDouble() const {
+  return AnimationUtils::TimeDurationToDouble(mStartTime, mRTPCallerType);
+}
+
+void Animation::SetStartTimeAsDouble(const Nullable<double>& aStartTime) {
+  return SetStartTime(AnimationUtils::DoubleToTimeDuration(aStartTime));
+}
+
+Nullable<double> Animation::GetCurrentTimeAsDouble() const {
+  return AnimationUtils::TimeDurationToDouble(GetCurrentTimeAsDuration(),
+                                              mRTPCallerType);
+}
+
+void Animation::SetCurrentTimeAsDouble(const Nullable<double>& aCurrentTime,
+                                       ErrorResult& aRv) {
+  if (aCurrentTime.IsNull()) {
+    if (!GetCurrentTimeAsDuration().IsNull()) {
+      aRv.ThrowTypeError(
+          "Current time is resolved but trying to set it to an unresolved "
+          "time");
+    }
+    return;
+  }
+
+  return SetCurrentTime(TimeDuration::FromMilliseconds(aCurrentTime.Value()));
+}
+
+// ---------------------------------------------------------------------------
+
+void Animation::Tick(AnimationTimeline::TickState& aTickState) {
+  if (Pending()) {
+    // Finish pending if we can, but make sure we've seen one existing tick, or
+    // we've requested to get started via SetPendingReadyTime.
+    if (!mPendingReadyTime.IsNull() || mSawTickWhilePending) {
+      TryTriggerNow();
+    }
+    mSawTickWhilePending = true;
+  }
+
+  UpdateTiming(SeekFlag::NoSeek, SyncNotifyFlag::Sync);
+
+  // Check for changes to whether or not this animation is replaceable.
+  bool isReplaceable = IsReplaceable();
+  if (isReplaceable && !mWasReplaceableAtLastTick) {
+    ScheduleReplacementCheck();
+  }
+  mWasReplaceableAtLastTick = isReplaceable;
+
+  if (!mEffect) {
+    return;
+  }
+
+  // Update layers if we are newly finished.
+  KeyframeEffect* keyframeEffect = mEffect->AsKeyframeEffect();
+  if (keyframeEffect && !keyframeEffect->Properties().IsEmpty() &&
+      !mFinishedAtLastComposeStyle &&
+      PlayState() == AnimationPlayState::Finished) {
+    PostUpdate();
+  }
+}
+
+bool Animation::TryTriggerNow() {
+  if (!Pending()) {
+    return true;
+  }
+  // If we don't have an active timeline we can't trigger the animation.
+  if (NS_WARN_IF(!mTimeline)) {
+    return false;
+  }
+  auto currentTime = mPendingReadyTime.IsNull()
+                         ? mTimeline->GetCurrentTimeAsDuration()
+                         : mTimeline->ToTimelineTime(mPendingReadyTime);
+  mPendingReadyTime = {};
+  if (NS_WARN_IF(currentTime.IsNull())) {
+    return false;
+  }
+  FinishPendingAt(currentTime.Value());
+  return true;
+}
+
+TimeStamp Animation::AnimationTimeToTimeStamp(
+    const StickyTimeDuration& aTime) const {
+  // Initializes to null. Return the same object every time to benefit from
+  // return-value-optimization.
+  TimeStamp result;
+
+  // We *don't* check for mTimeline->TracksWallclockTime() here because that
+  // method only tells us if the timeline times can be converted to
+  // TimeStamps that can be compared to TimeStamp::Now() or not, *not*
+  // whether the timelines can be converted to TimeStamp values at all.
+  //
+  // Furthermore, we want to be able to use this method when the refresh driver
+  // is under test control (in which case TracksWallclockTime() will return
+  // false).
+  //
+  // Once we introduce timelines that are not time-based we will need to
+  // differentiate between them here and determine how to sort their events.
+  if (!mTimeline) {
+    return result;
+  }
+
+  // Check the time is convertible to a timestamp
+  if (aTime == TimeDuration::Forever() || mPlaybackRate == 0.0 ||
+      mStartTime.IsNull()) {
+    return result;
+  }
+
+  // Invert the standard relation:
+  //   current time = (timeline time - start time) * playback rate
+  TimeDuration timelineTime =
+      TimeDuration(aTime).MultDouble(1.0 / mPlaybackRate) + mStartTime.Value();
+
+  result = mTimeline->ToTimeStamp(timelineTime);
+  return result;
+}
+
+TimeStamp Animation::ElapsedTimeToTimeStamp(
+    const StickyTimeDuration& aElapsedTime) const {
+  TimeDuration delay =
+      mEffect ? mEffect->NormalizedTiming().Delay() : TimeDuration();
+  return AnimationTimeToTimeStamp(aElapsedTime + delay);
+}
+
+// https://drafts.csswg.org/web-animations/#silently-set-the-current-time
+void Animation::SilentlySetCurrentTime(const TimeDuration& aSeekTime) {
+  // TODO: Bug 1762238: Introduce "valid seek time" after introducing
+  // CSSNumberish time values.
+  // https://drafts.csswg.org/web-animations-2/#silently-set-the-current-time
+
+  if (!mHoldTime.IsNull() || mStartTime.IsNull() || !mTimeline ||
+      mTimeline->GetCurrentTimeAsDuration().IsNull() || mPlaybackRate == 0.0) {
+    mHoldTime.SetValue(aSeekTime);
+  } else {
+    mStartTime =
+        StartTimeFromTimelineTime(mTimeline->GetCurrentTimeAsDuration().Value(),
+                                  aSeekTime, mPlaybackRate);
+  }
+
+  if (!mTimeline || mTimeline->GetCurrentTimeAsDuration().IsNull()) {
+    mStartTime.SetNull();
+  }
+
+  mPreviousCurrentTime.SetNull();
+  mResetCurrentTimeOnResume = false;
+}
+
+bool Animation::ShouldBeSynchronizedWithMainThread(
+    const nsCSSPropertyIDSet& aPropertySet, const nsIFrame* aFrame,
+    AnimationPerformanceWarning::Type& aPerformanceWarning) const {
+  // Only synchronize playing animations
+  if (!IsPlaying()) {
+    return false;
+  }
+
+  // Currently only transform animations need to be synchronized
+  if (!aPropertySet.Intersects(nsCSSPropertyIDSet::TransformLikeProperties())) {
+    return false;
+  }
+
+  KeyframeEffect* keyframeEffect =
+      mEffect ? mEffect->AsKeyframeEffect() : nullptr;
+  if (!keyframeEffect) {
+    return false;
+  }
+
+  return keyframeEffect->ShouldBlockAsyncTransformAnimations(
+      aFrame, aPropertySet, aPerformanceWarning);
+}
+
+void Animation::UpdateRelevance() {
+  bool wasRelevant = mIsRelevant;
+  mIsRelevant = mReplaceState != AnimationReplaceState::Removed &&
+                (HasCurrentEffect() || IsInEffect());
+
+  // Notify animation observers.
+  if (wasRelevant && !mIsRelevant) {
+    MutationObservers::NotifyAnimationRemoved(this);
+  } else if (!wasRelevant && mIsRelevant) {
+    UpdateHiddenByContentVisibility();
+    MutationObservers::NotifyAnimationAdded(this);
+  }
+}
+
+template <class T>
+bool IsMarkupAnimation(T* aAnimation) {
+  return aAnimation && aAnimation->IsTiedToMarkup();
+}
+
+// https://drafts.csswg.org/web-animations/#replaceable-animation
+bool Animation::IsReplaceable() const {
+  // We never replace CSS animations or CSS transitions since they are managed
+  // by CSS.
+  if (IsMarkupAnimation(AsCSSAnimation()) ||
+      IsMarkupAnimation(AsCSSTransition())) {
+    return false;
+  }
+
+  // Only finished animations can be replaced.
+  if (PlayState() != AnimationPlayState::Finished) {
+    return false;
+  }
+
+  // Already removed animations cannot be replaced.
+  if (ReplaceState() == AnimationReplaceState::Removed) {
+    return false;
+  }
+
+  // We can only replace an animation if we know that, uninterfered, it would
+  // never start playing again. That excludes any animations on timelines that
+  // aren't monotonically increasing.
+  //
+  // If we don't have any timeline at all, then we can't be in the finished
+  // state (since we need both a resolved start time and current time for that)
+  // and will have already returned false above.
+  //
+  // (However, if it ever does become possible to be finished without a timeline
+  // then we will want to return false here since it probably suggests an
+  // animation being driven directly by script, in which case we can't assume
+  // anything about how they will behave.)
+  if (!GetTimeline() || !GetTimeline()->TracksWallclockTime()) {
+    return false;
+  }
+
+  // If the animation doesn't have an effect then we can't determine if it is
+  // filling or not so just leave it alone.
+  if (!GetEffect()) {
+    return false;
+  }
+
+  // At the time of writing we only know about KeyframeEffects. If we introduce
+  // other types of effects we will need to decide if they are replaceable or
+  // not.
+  MOZ_ASSERT(GetEffect()->AsKeyframeEffect(),
+             "Effect should be a keyframe effect");
+
+  // We only replace animations that are filling.
+  if (GetEffect()->GetComputedTiming().mProgress.IsNull()) {
+    return false;
+  }
+
+  // We should only replace animations with a target element (since otherwise
+  // what other effects would we consider when determining if they are covered
+  // or not?).
+  if (!GetEffect()->AsKeyframeEffect()->GetAnimationTarget()) {
+    return false;
+  }
+
+  return true;
+}
+
+bool Animation::IsRemovable() const {
+  return ReplaceState() == AnimationReplaceState::Active && IsReplaceable();
+}
+
+void Animation::ScheduleReplacementCheck() {
+  MOZ_ASSERT(
+      IsReplaceable(),
+      "Should only schedule a replacement check for a replaceable animation");
+
+  // If IsReplaceable() is true, the following should also hold
+  MOZ_ASSERT(GetEffect());
+  MOZ_ASSERT(GetEffect()->AsKeyframeEffect());
+
+  NonOwningAnimationTarget target =
+      GetEffect()->AsKeyframeEffect()->GetAnimationTarget();
+
+  MOZ_ASSERT(target);
+
+  nsPresContext* presContext =
+      nsContentUtils::GetContextForContent(target.mElement);
+  if (presContext) {
+    presContext->EffectCompositor()->NoteElementForReducing(target);
+  }
+}
+
+void Animation::MaybeScheduleReplacementCheck() {
+  if (!IsReplaceable()) {
+    return;
+  }
+
+  ScheduleReplacementCheck();
+}
+
+void Animation::Remove() {
+  MOZ_ASSERT(IsRemovable(),
+             "Should not be trying to remove an effect that is not removable");
+
+  mReplaceState = AnimationReplaceState::Removed;
+
+  UpdateEffect(PostRestyleMode::IfNeeded);
+  PostUpdate();
+
+  QueuePlaybackEvent(u"remove"_ns, GetTimelineCurrentTimeAsTimeStamp());
+}
+
+bool Animation::HasLowerCompositeOrderThan(const Animation& aOther) const {
+  // 0. Object-equality case
+  if (&aOther == this) {
+    return false;
+  }
+
+  // 1. CSS Transitions sort lowest
+  {
+    auto asCSSTransitionForSorting =
+        [](const Animation& anim) -> const CSSTransition* {
+      const CSSTransition* transition = anim.AsCSSTransition();
+      return transition && transition->IsTiedToMarkup() ? transition : nullptr;
+    };
+    auto thisTransition = asCSSTransitionForSorting(*this);
+    auto otherTransition = asCSSTransitionForSorting(aOther);
+    if (thisTransition && otherTransition) {
+      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;
+    }
+  }
+
+  // 2. CSS Animations sort next
+  {
+    auto asCSSAnimationForSorting =
+        [](const Animation& anim) -> const CSSAnimation* {
+      const CSSAnimation* animation = anim.AsCSSAnimation();
+      return animation && animation->IsTiedToMarkup() ? animation : nullptr;
+    };
+    auto thisAnimation = asCSSAnimationForSorting(*this);
+    auto otherAnimation = asCSSAnimationForSorting(aOther);
+    if (thisAnimation && otherAnimation) {
+      return thisAnimation->HasLowerCompositeOrderThan(*otherAnimation);
+    }
+    if (thisAnimation || otherAnimation) {
+      return thisAnimation;
+    }
+  }
+
+  // Subclasses of Animation repurpose mAnimationIndex to implement their
+  // own brand of composite ordering. However, by this point we should have
+  // handled any such custom composite ordering so we should now have unique
+  // animation indices.
+  MOZ_ASSERT(mAnimationIndex != aOther.mAnimationIndex,
+             "Animation indices should be unique");
+
+  // 3. Finally, generic animations sort by their position in the global
+  // animation array.
+  return mAnimationIndex < aOther.mAnimationIndex;
+}
+
+void Animation::WillComposeStyle() {
+  mFinishedAtLastComposeStyle = (PlayState() == AnimationPlayState::Finished);
+
+  MOZ_ASSERT(mEffect);
+
+  KeyframeEffect* keyframeEffect = mEffect->AsKeyframeEffect();
+  if (keyframeEffect) {
+    keyframeEffect->WillComposeStyle();
+  }
+}
+
+void Animation::ComposeStyle(StyleAnimationValueMap& aComposeResult,
+                             const nsCSSPropertyIDSet& aPropertiesToSkip) {
+  if (!mEffect) {
+    return;
+  }
+
+  // In order to prevent flicker, there are a few cases where we want to use
+  // a different time for rendering that would otherwise be returned by
+  // GetCurrentTimeAsDuration. These are:
+  //
+  // (a) For animations that are pausing but which are still running on the
+  //     compositor. In this case we send a layer transaction that removes the
+  //     animation but which also contains the animation values calculated on
+  //     the main thread. To prevent flicker when this occurs we want to ensure
+  //     the timeline time used to calculate the main thread animation values
+  //     does not lag far behind the time used on the compositor. Ideally we
+  //     would like to use the "animation ready time", but for now we just use
+  //     the current wallclock time. TODO(emilio): After bug 1864425 it seems we
+  //     could just use the ready time, or maybe we can remove this?
+  //
+  // (b) For animations that are pausing that we have already taken off the
+  //     compositor. In this case we record a pending ready time but we don't
+  //     apply it until the next tick. However, while waiting for the next tick,
+  //     we should still use the pending ready time as the timeline time. If we
+  //     use the regular timeline time the animation may appear jump backwards
+  //     if the main thread's timeline time lags behind the compositor.
+  //
+  // (c) For animations that are play-pending due to an aborted pause operation
+  //     (i.e. a pause operation that was interrupted before we entered the
+  //     paused state). When we cancel a pending pause we might momentarily take
+  //     the animation off the compositor, only to re-add it moments later. In
+  //     that case the compositor might have been ahead of the main thread so we
+  //     should use the current wallclock time to ensure the animation doesn't
+  //     temporarily jump backwards.
+  //
+  // To address each of these cases we temporarily tweak the hold time
+  // immediately before updating the style rule and then restore it immediately
+  // afterwards. This is purely to prevent visual flicker. Other behavior
+  // such as dispatching events continues to rely on the regular timeline time.
+  const bool pending = Pending();
+  {
+    AutoRestore<Nullable<TimeDuration>> restoreHoldTime(mHoldTime);
+    if (pending && mHoldTime.IsNull() && !mStartTime.IsNull()) {
+      Nullable<TimeDuration> timeToUse;
+      if (mTimeline && mTimeline->TracksWallclockTime()) {
+        timeToUse = mTimeline->ToTimelineTime(TimeStamp::Now());
+      }
+      if (!timeToUse.IsNull()) {
+        mHoldTime = CurrentTimeFromTimelineTime(
+            timeToUse.Value(), mStartTime.Value(), mPlaybackRate);
+      }
+    }
+
+    KeyframeEffect* keyframeEffect = mEffect->AsKeyframeEffect();
+    if (keyframeEffect) {
+      keyframeEffect->ComposeStyle(aComposeResult, aPropertiesToSkip);
+    }
+  }
+
+  MOZ_ASSERT(
+      pending == Pending(),
+      "Pending state should not change during the course of compositing");
+}
+
+void Animation::NotifyEffectTimingUpdated() {
+  MOZ_ASSERT(mEffect,
+             "We should only update effect timing when we have a target "
+             "effect");
+  UpdateTiming(Animation::SeekFlag::NoSeek, Animation::SyncNotifyFlag::Async);
+}
+
+void Animation::NotifyEffectPropertiesUpdated() {
+  MOZ_ASSERT(mEffect,
+             "We should only update effect properties when we have a target "
+             "effect");
+
+  MaybeScheduleReplacementCheck();
+}
+
+void Animation::NotifyEffectTargetUpdated() {
+  MOZ_ASSERT(mEffect,
+             "We should only update the effect target when we have a target "
+             "effect");
+
+  MaybeScheduleReplacementCheck();
+}
+
+static bool EnsurePaintIsScheduled(Document& aDoc) {
+  PresShell* presShell = aDoc.GetPresShell();
+  if (!presShell) {
+    return false;
+  }
+  nsIFrame* rootFrame = presShell->GetRootFrame();
+  if (!rootFrame) {
+    return false;
+  }
+  rootFrame->SchedulePaintWithoutInvalidatingObservers();
+  return rootFrame->PresContext()->RefreshDriver()->IsInRefresh();
+}
+
+// https://drafts.csswg.org/web-animations/#play-an-animation
+void Animation::PlayNoUpdate(ErrorResult& aRv, LimitBehavior aLimitBehavior) {
+  AutoMutationBatchForAnimation mb(*this);
+
+  const bool isAutoRewind = aLimitBehavior == LimitBehavior::AutoRewind;
+  const bool abortedPause = mPendingState == PendingState::PausePending;
+  double effectivePlaybackRate = CurrentOrPendingPlaybackRate();
+
+  Nullable<TimeDuration> currentTime = GetCurrentTimeAsDuration();
+  if (mResetCurrentTimeOnResume) {
+    currentTime.SetNull();
+    mResetCurrentTimeOnResume = false;
+  }
+
+  Nullable<TimeDuration> seekTime;
+  if (isAutoRewind) {
+    if (effectivePlaybackRate >= 0.0 &&
+        (currentTime.IsNull() || currentTime.Value() < TimeDuration() ||
+         currentTime.Value() >= EffectEnd())) {
+      seekTime.SetValue(TimeDuration());
+    } else if (effectivePlaybackRate < 0.0 &&
+               (currentTime.IsNull() || currentTime.Value() <= TimeDuration() ||
+                currentTime.Value() > EffectEnd())) {
+      if (EffectEnd() == TimeDuration::Forever()) {
+        return aRv.ThrowInvalidStateError(
+            "Can't rewind animation with infinite effect end");
+      }
+      seekTime.SetValue(TimeDuration(EffectEnd()));
+    }
+  }
+
+  if (seekTime.IsNull() && mStartTime.IsNull() && currentTime.IsNull()) {
+    seekTime.SetValue(TimeDuration());
+  }
+
+  if (!seekTime.IsNull()) {
+    if (HasFiniteTimeline()) {
+      mStartTime = seekTime;
+      mHoldTime.SetNull();
+      ApplyPendingPlaybackRate();
+    } else {
+      mHoldTime = seekTime;
+    }
+  }
+
+  bool reuseReadyPromise = false;
+  if (mPendingState != PendingState::NotPending) {
+    CancelPendingTasks();
+    reuseReadyPromise = true;
+  }
+
+  // If the hold time is null then we're already playing normally and,
+  // typically, we can bail out here.
+  //
+  // However, there are two cases where we can't do that:
+  //
+  // (a) If we just aborted a pause. In this case, for consistency, we need to
+  //     go through the motions of doing an asynchronous start.
+  //
+  // (b) If we have timing changes (specifically a change to the playbackRate)
+  //     that should be applied asynchronously.
+  //
+  if (mHoldTime.IsNull() && seekTime.IsNull() && !abortedPause &&
+      !mPendingPlaybackRate) {
+    return;
+  }
+
+  // Clear the start time until we resolve a new one. We do this except
+  // for the case where we are aborting a pause and don't have a hold time.
+  //
+  // If we're aborting a pause and *do* have a hold time (e.g. because
+  // the animation is finished or we just applied the auto-rewind behavior
+  // above) we should respect it by clearing the start time. If we *don't*
+  // have a hold time we should keep the current start time so that the
+  // the animation continues moving uninterrupted by the aborted pause.
+  //
+  // (If we're not aborting a pause, mHoldTime must be resolved by now
+  //  or else we would have returned above.)
+  if (!mHoldTime.IsNull()) {
+    mStartTime.SetNull();
+  }
+
+  if (!reuseReadyPromise) {
+    // Clear ready promise. We'll create a new one lazily.
+    mReady = nullptr;
+  }
+
+  mPendingState = PendingState::PlayPending;
+  mPendingReadyTime = {};
+  mSawTickWhilePending = false;
+  if (Document* doc = GetRenderedDocument()) {
+    if (HasFiniteTimeline()) {
+      // Always schedule a task even if we would like to let this animation
+      // immediately ready, per spec.
+      // https://drafts.csswg.org/web-animations/#playing-an-animation-section
+      // If there's no rendered document, we fail to track this animation, so
+      // let the scroll frame to trigger it when ticking.
+      doc->GetOrCreateScrollTimelineAnimationTracker()->AddPending(*this);
+    }
+    // Make sure to try to schedule a tick.
+    mSawTickWhilePending = EnsurePaintIsScheduled(*doc);
+  }
+
+  UpdateTiming(SeekFlag::NoSeek, SyncNotifyFlag::Async);
+  if (IsRelevant()) {
+    MutationObservers::NotifyAnimationChanged(this);
+  }
+}
+
+// https://drafts.csswg.org/web-animations/#pause-an-animation
+void Animation::Pause(ErrorResult& aRv) {
+  if (IsPausedOrPausing()) {
+    return;
+  }
+
+  AutoMutationBatchForAnimation mb(*this);
+
+  Nullable<TimeDuration> seekTime;
+  // If we are transitioning from idle, fill in the current time
+  if (GetCurrentTimeAsDuration().IsNull()) {
+    if (mPlaybackRate >= 0.0) {
+      seekTime.SetValue(TimeDuration(0));
+    } else {
+      if (EffectEnd() == TimeDuration::Forever()) {
+        return aRv.ThrowInvalidStateError("Can't seek to infinite effect end");
+      }
+      seekTime.SetValue(TimeDuration(EffectEnd()));
+    }
+  }
+
+  if (!seekTime.IsNull()) {
+    if (HasFiniteTimeline()) {
+      mStartTime = seekTime;
+    } else {
+      mHoldTime = seekTime;
+    }
+  }
+
+  bool reuseReadyPromise = false;
+  if (mPendingState == PendingState::PlayPending) {
+    CancelPendingTasks();
+    reuseReadyPromise = true;
+  }
+
+  if (!reuseReadyPromise) {
+    // Clear ready promise. We'll create a new one lazily.
+    mReady = nullptr;
+  }
+
+  mPendingState = PendingState::PausePending;
+  mPendingReadyTime = {};
+  mSawTickWhilePending = false;
+
+  // See the relevant PlayPending code for comments.
+  if (Document* doc = GetRenderedDocument()) {
+    if (HasFiniteTimeline()) {
+      doc->GetOrCreateScrollTimelineAnimationTracker()->AddPending(*this);
+    }
+    mSawTickWhilePending = EnsurePaintIsScheduled(*doc);
+  }
+
+  UpdateTiming(SeekFlag::NoSeek, SyncNotifyFlag::Async);
+  if (IsRelevant()) {
+    MutationObservers::NotifyAnimationChanged(this);
+  }
+
+  PostUpdate();
+}
+
+// https://drafts.csswg.org/web-animations/#play-an-animation
+void Animation::ResumeAt(const TimeDuration& aReadyTime) {
+  // This method is only expected to be called for an animation that is
+  // waiting to play. We can easily adapt it to handle other states
+  // but it's currently not necessary.
+  MOZ_ASSERT(mPendingState == PendingState::PlayPending,
+             "Expected to resume a play-pending animation");
+  MOZ_ASSERT(!mHoldTime.IsNull() || !mStartTime.IsNull(),
+             "An animation in the play-pending state should have either a"
+             " resolved hold time or resolved start time");
+
+  AutoMutationBatchForAnimation mb(*this);
+  bool hadPendingPlaybackRate = mPendingPlaybackRate.isSome();
+
+  if (!mHoldTime.IsNull()) {
+    // The hold time is set, so we don't need any special handling to preserve
+    // the current time.
+    ApplyPendingPlaybackRate();
+    mStartTime =
+        StartTimeFromTimelineTime(aReadyTime, mHoldTime.Value(), mPlaybackRate);
+    if (mPlaybackRate != 0) {
+      mHoldTime.SetNull();
+    }
+  } else if (!mStartTime.IsNull() && mPendingPlaybackRate) {
+    // Apply any pending playback rate, preserving the current time.
+    TimeDuration currentTimeToMatch = CurrentTimeFromTimelineTime(
+        aReadyTime, mStartTime.Value(), mPlaybackRate);
+    ApplyPendingPlaybackRate();
+    mStartTime = StartTimeFromTimelineTime(aReadyTime, currentTimeToMatch,
+                                           mPlaybackRate);
+    if (mPlaybackRate == 0) {
+      mHoldTime.SetValue(currentTimeToMatch);
+    }
+  }
+
+  mPendingState = PendingState::NotPending;
+
+  UpdateTiming(SeekFlag::NoSeek, SyncNotifyFlag::Sync);
+
+  // If we had a pending playback rate, we will have now applied it so we need
+  // to notify observers.
+  if (hadPendingPlaybackRate && IsRelevant()) {
+    MutationObservers::NotifyAnimationChanged(this);
+  }
+
+  if (mReady) {
+    mReady->MaybeResolve(this);
+  }
+}
+
+void Animation::PauseAt(const TimeDuration& aReadyTime) {
+  MOZ_ASSERT(mPendingState == PendingState::PausePending,
+             "Expected to pause a pause-pending animation");
+
+  if (!mStartTime.IsNull() && mHoldTime.IsNull()) {
+    mHoldTime = CurrentTimeFromTimelineTime(aReadyTime, mStartTime.Value(),
+                                            mPlaybackRate);
+  }
+  ApplyPendingPlaybackRate();
+  mStartTime.SetNull();
+  mPendingState = PendingState::NotPending;
+
+  UpdateTiming(SeekFlag::NoSeek, SyncNotifyFlag::Async);
+
+  if (mReady) {
+    mReady->MaybeResolve(this);
+  }
+}
+
+void Animation::UpdateTiming(SeekFlag aSeekFlag,
+                             SyncNotifyFlag aSyncNotifyFlag) {
+  // We call UpdateFinishedState before UpdateEffect because the former
+  // can change the current time, which is used by the latter.
+  UpdateFinishedState(aSeekFlag, aSyncNotifyFlag);
+  UpdateEffect(PostRestyleMode::IfNeeded);
+
+  if (mTimeline) {
+    mTimeline->NotifyAnimationUpdated(*this);
+  }
+}
+
+// https://drafts.csswg.org/web-animations/#update-an-animations-finished-state
+void Animation::UpdateFinishedState(SeekFlag aSeekFlag,
+                                    SyncNotifyFlag aSyncNotifyFlag) {
+  Nullable<TimeDuration> unconstrainedCurrentTime =
+      aSeekFlag == SeekFlag::NoSeek ? GetUnconstrainedCurrentTime()
+                                    : GetCurrentTimeAsDuration();
+  TimeDuration effectEnd = TimeDuration(EffectEnd());
+
+  if (!unconstrainedCurrentTime.IsNull() && !mStartTime.IsNull() &&
+      mPendingState == PendingState::NotPending) {
+    if (mPlaybackRate > 0.0 && unconstrainedCurrentTime.Value() >= effectEnd) {
+      if (aSeekFlag == SeekFlag::DidSeek) {
+        mHoldTime = unconstrainedCurrentTime;
+      } else if (!mPreviousCurrentTime.IsNull()) {
+        mHoldTime.SetValue(std::max(mPreviousCurrentTime.Value(), effectEnd));
+      } else {
+        mHoldTime.SetValue(effectEnd);
+      }
+    } else if (mPlaybackRate < 0.0 &&
+               unconstrainedCurrentTime.Value() <= TimeDuration()) {
+      if (aSeekFlag == SeekFlag::DidSeek) {
+        mHoldTime = unconstrainedCurrentTime;
+      } else if (!mPreviousCurrentTime.IsNull()) {
+        mHoldTime.SetValue(
+            std::min(mPreviousCurrentTime.Value(), TimeDuration(0)));
+      } else {
+        mHoldTime.SetValue(0);
+      }
+    } else if (mPlaybackRate != 0.0 && mTimeline &&
+               !mTimeline->GetCurrentTimeAsDuration().IsNull()) {
+      if (aSeekFlag == SeekFlag::DidSeek && !mHoldTime.IsNull()) {
+        mStartTime = StartTimeFromTimelineTime(
+            mTimeline->GetCurrentTimeAsDuration().Value(), mHoldTime.Value(),
+            mPlaybackRate);
+      }
+      mHoldTime.SetNull();
+    }
+  }
+
+  // We must recalculate the current time to take account of any mHoldTime
+  // changes the code above made.
+  mPreviousCurrentTime = GetCurrentTimeAsDuration();
+
+  bool currentFinishedState = PlayState() == AnimationPlayState::Finished;
+  if (currentFinishedState && !mFinishedIsResolved) {
+    DoFinishNotification(aSyncNotifyFlag);
+  } else if (!currentFinishedState && mFinishedIsResolved) {
+    ResetFinishedPromise();
+  }
+}
+
+void Animation::UpdateEffect(PostRestyleMode aPostRestyle) {
+  if (mEffect) {
+    UpdateRelevance();
+
+    KeyframeEffect* keyframeEffect = mEffect->AsKeyframeEffect();
+    if (keyframeEffect) {
+      keyframeEffect->NotifyAnimationTimingUpdated(aPostRestyle);
+    }
+  }
+}
+
+void Animation::FlushUnanimatedStyle() const {
+  if (Document* doc = GetRenderedDocument()) {
+    doc->FlushPendingNotifications(
+        ChangesToFlush(FlushType::Style, false /* flush animations */));
+  }
+}
+
+void Animation::PostUpdate() {
+  if (!mEffect) {
+    return;
+  }
+
+  KeyframeEffect* keyframeEffect = mEffect->AsKeyframeEffect();
+  if (!keyframeEffect) {
+    return;
+  }
+  keyframeEffect->RequestRestyle(EffectCompositor::RestyleType::Layer);
+}
+
+void Animation::CancelPendingTasks() {
+  mPendingState = PendingState::NotPending;
+}
+
+// https://drafts.csswg.org/web-animations/#reset-an-animations-pending-tasks
+void Animation::ResetPendingTasks() {
+  if (!Pending()) {
+    return;
+  }
+
+  CancelPendingTasks();
+  ApplyPendingPlaybackRate();
+
+  if (mReady) {
+    mReady->MaybeReject(NS_ERROR_DOM_ABORT_ERR);
+    MOZ_ALWAYS_TRUE(mReady->SetAnyPromiseIsHandled());
+    mReady = nullptr;
+  }
+}
+
+// https://drafts.csswg.org/web-animations-2/#at-progress-timeline-boundary
+/* static*/ Animation::ProgressTimelinePosition
+Animation::AtProgressTimelineBoundary(
+    const Nullable<TimeDuration>& aTimelineDuration,
+    const Nullable<TimeDuration>& aCurrentTime,
+    const TimeDuration& aEffectStartTime, const double aPlaybackRate) {
+  // Based on changed defined in: https://github.com/w3c/csswg-drafts/pull/6702
+  // 1.  If any of the following conditions are true:
+  //     * the associated animation's timeline is not a progress-based timeline,
+  //     or
+  //     * the associated animation's timeline duration is unresolved or zero,
+  //     or
+  //     * the animation's playback rate is zero
+  //     return false
+  // Note: We can detect a progress-based timeline by relying on the fact that
+  // monotonic timelines (i.e. non-progress-based timelines) have an unresolved
+  // timeline duration.
+  if (aTimelineDuration.IsNull() || aTimelineDuration.Value().IsZero() ||
+      aPlaybackRate == 0.0) {
+    return ProgressTimelinePosition::NotBoundary;
+  }
+
+  // 2.  Let effective start time be the animation's start time if resolved, or
+  // zero otherwise.
+  const TimeDuration& effectiveStartTime = aEffectStartTime;
+
+  // 3.  Let effective timeline time be (animation's current time / animation's
+  // playback rate) + effective start time.
+  // Note: we use zero if the current time is unresolved. See the spec issue:
+  // https://github.com/w3c/csswg-drafts/issues/7458
+  const TimeDuration effectiveTimelineTime =
+      (aCurrentTime.IsNull()
+           ? TimeDuration()
+           : aCurrentTime.Value().MultDouble(1.0 / aPlaybackRate)) +
+      effectiveStartTime;
+
+  // 4.  Let effective timeline progress be (effective timeline time / timeline
+  // duration)
+  // 5.  If effective timeline progress is 0 or 1, return true,
+  // We avoid the division here but it is effectively the same as 4 & 5 above.
+  return effectiveTimelineTime.IsZero() ||
+                 (AnimationUtils::IsWithinAnimationTimeTolerance(
+                     effectiveTimelineTime, aTimelineDuration.Value()))
+             ? ProgressTimelinePosition::Boundary
+             : ProgressTimelinePosition::NotBoundary;
+}
+
+StickyTimeDuration Animation::EffectEnd() const {
+  if (!mEffect) {
+    return StickyTimeDuration(0);
+  }
+
+  return mEffect->NormalizedTiming().EndTime();
+}
+
+Document* Animation::GetRenderedDocument() const {
+  if (!mEffect || !mEffect->AsKeyframeEffect()) {
+    return nullptr;
+  }
+
+  return mEffect->AsKeyframeEffect()->GetRenderedDocument();
+}
+
+Document* Animation::GetTimelineDocument() const {
+  return mTimeline ? mTimeline->GetDocument() : nullptr;
+}
+
+void Animation::UpdateScrollTimelineAnimationTracker(
+    AnimationTimeline* aOldTimeline, AnimationTimeline* aNewTimeline) {
+  // If we are still in pending, we may have to move this animation into the
+  // correct animation tracker.
+  Document* doc = GetRenderedDocument();
+  if (!doc || !Pending()) {
+    return;
+  }
+
+  const bool fromFiniteTimeline =
+      aOldTimeline && !aOldTimeline->IsMonotonicallyIncreasing();
+  const bool toFiniteTimeline =
+      aNewTimeline && !aNewTimeline->IsMonotonicallyIncreasing();
+  if (fromFiniteTimeline == toFiniteTimeline) {
+    return;
+  }
+
+  if (toFiniteTimeline) {
+    doc->GetOrCreateScrollTimelineAnimationTracker()->AddPending(*this);
+  } else {
+    // From scroll-timeline to null/document-timeline
+    if (auto* tracker = doc->GetScrollTimelineAnimationTracker()) {
+      tracker->RemovePending(*this);
+    }
+    EnsurePaintIsScheduled(*doc);
+  }
+}
+
+class AsyncFinishNotification : public MicroTaskRunnable {
+ public:
+  explicit AsyncFinishNotification(Animation* aAnimation)
+      : mAnimation(aAnimation) {}
+
+  virtual void Run(AutoSlowOperation& aAso) override {
+    mAnimation->DoFinishNotificationImmediately(this);
+    mAnimation = nullptr;
+  }
+
+  virtual bool Suppressed() override {
+    nsIGlobalObject* global = mAnimation->GetOwnerGlobal();
+    return global && global->IsInSyncOperation();
+  }
+
+ private:
+  RefPtr<Animation> mAnimation;
+};
+
+void Animation::DoFinishNotification(SyncNotifyFlag aSyncNotifyFlag) {
+  CycleCollectedJSContext* context = CycleCollectedJSContext::Get();
+
+  if (aSyncNotifyFlag == SyncNotifyFlag::Sync) {
+    DoFinishNotificationImmediately();
+  } else if (!mFinishNotificationTask) {
+    RefPtr<MicroTaskRunnable> runnable = new AsyncFinishNotification(this);
+    context->DispatchToMicroTask(do_AddRef(runnable));
+    mFinishNotificationTask = std::move(runnable);
+  }
+}
+
+void Animation::ResetFinishedPromise() {
+  mFinishedIsResolved = false;
+  mFinished = nullptr;
+}
+
+void Animation::MaybeResolveFinishedPromise() {
+  if (mFinished) {
+    mFinished->MaybeResolve(this);
+  }
+  mFinishedIsResolved = true;
+}
+
+void Animation::DoFinishNotificationImmediately(MicroTaskRunnable* aAsync) {
+  if (aAsync && aAsync != mFinishNotificationTask) {
+    return;
+  }
+
+  mFinishNotificationTask = nullptr;
+
+  if (PlayState() != AnimationPlayState::Finished) {
+    return;
+  }
+
+  MaybeResolveFinishedPromise();
+
+  QueuePlaybackEvent(u"finish"_ns, AnimationTimeToTimeStamp(EffectEnd()));
+}
+
+void Animation::QueuePlaybackEvent(const nsAString& aName,
+                                   TimeStamp&& aScheduledEventTime) {
+  // Use document for timing.
+  // https://drafts.csswg.org/web-animations-1/#document-for-timing
+  Document* doc = GetTimelineDocument();
+  if (!doc) {
+    return;
+  }
+
+  nsPresContext* presContext = doc->GetPresContext();
+  if (!presContext) {
+    return;
+  }
+
+  AnimationPlaybackEventInit init;
+  if (aName.EqualsLiteral("finish") || aName.EqualsLiteral("remove")) {
+    init.mCurrentTime = GetCurrentTimeAsDouble();
+  }
+  if (mTimeline) {
+    init.mTimelineTime = mTimeline->GetCurrentTimeAsDouble();
+  }
+
+  RefPtr<AnimationPlaybackEvent> event =
+      AnimationPlaybackEvent::Constructor(this, aName, init);
+  event->SetTrusted(true);
+
+  presContext->AnimationEventDispatcher()->QueueEvent(AnimationEventInfo(
+      std::move(event), std::move(aScheduledEventTime), this));
+}
+
+bool Animation::IsRunningOnCompositor() const {
+  return mEffect && mEffect->AsKeyframeEffect() &&
+         mEffect->AsKeyframeEffect()->IsRunningOnCompositor();
+}
+
+bool Animation::HasCurrentEffect() const {
+  return GetEffect() && GetEffect()->IsCurrent();
+}
+
+bool Animation::IsInEffect() const {
+  return GetEffect() && GetEffect()->IsInEffect();
+}
+
+void Animation::SetHiddenByContentVisibility(bool hidden) {
+  if (mHiddenByContentVisibility == hidden) {
+    return;
+  }
+
+  mHiddenByContentVisibility = hidden;
+
+  if (!GetTimeline()) {
+    return;
+  }
+
+  GetTimeline()->NotifyAnimationContentVisibilityChanged(this, !hidden);
+}
+
+void Animation::UpdateHiddenByContentVisibility() {
+  // To be consistent with nsIFrame::UpdateAnimationVisibility, here we only
+  // deal with CSSAnimation and CSSTransition.
+  if (!AsCSSAnimation() && !AsCSSTransition()) {
+    return;
+  }
+  NonOwningAnimationTarget target = GetTargetForAnimation();
+  if (!target) {
+    return;
+  }
+  // If a CSS animation or CSS transition is no longer associated with an owning
+  // element, it behaves like a programmatic web animation, c-v shouldn't hide
+  // it.
+  bool hasOwningElement = IsMarkupAnimation(AsCSSAnimation()) ||
+                          IsMarkupAnimation(AsCSSTransition());
+  if (auto* frame = target.mElement->GetPrimaryFrame()) {
+    SetHiddenByContentVisibility(
+        hasOwningElement && frame->IsHiddenByContentVisibilityOnAnyAncestor());
+  }
+}
+
+StickyTimeDuration Animation::IntervalStartTime(
+    const StickyTimeDuration& aActiveDuration) const {
+  MOZ_ASSERT(AsCSSTransition() || AsCSSAnimation(),
+             "Should be called for CSS animations or transitions");
+  static constexpr StickyTimeDuration zeroDuration = StickyTimeDuration();
+  return std::max(
+      std::min(StickyTimeDuration(-mEffect->NormalizedTiming().Delay()),
+               aActiveDuration),
+      zeroDuration);
+}
+
+// Later side of the elapsed time range reported in CSS Animations and CSS
+// Transitions events.
+//
+// https://drafts.csswg.org/css-animations-2/#interval-end
+// https://drafts.csswg.org/css-transitions-2/#interval-end
+StickyTimeDuration Animation::IntervalEndTime(
+    const StickyTimeDuration& aActiveDuration) const {
+  MOZ_ASSERT(AsCSSTransition() || AsCSSAnimation(),
+             "Should be called for CSS animations or transitions");
+
+  static constexpr StickyTimeDuration zeroDuration = StickyTimeDuration();
+  const StickyTimeDuration& effectEnd = EffectEnd();
+
+  // If both "associated effect end" and "start delay" are Infinity, we skip it
+  // because we will get NaN when computing "Infinity - Infinity", and
+  // using NaN in std::min or std::max is undefined.
+  if (MOZ_UNLIKELY(effectEnd == TimeDuration::Forever() &&
+                   effectEnd == mEffect->NormalizedTiming().Delay())) {
+    // Note: If we use TimeDuration::Forever(), within our animation event
+    // handling, we'd end up turning that into a null TimeStamp which can causes
+    // errors if we try to do any arithmetic with it. Given that we should never
+    // end up _using_ the interval end time. So returning zeroDuration here is
+    // probably fine.
+    return zeroDuration;
+  }
+
+  return std::max(std::min(effectEnd - mEffect->NormalizedTiming().Delay(),
+                           aActiveDuration),
+                  zeroDuration);
+}
+
+}  // namespace mozilla::dom