[AnimationWorklet] Update TODO regarding WorkletAnimation's direction and current time

WorkletAnimation supports negative playback rate (crrev.com/c/1423537)
now. However, the playback rate is not used when calculating the current
time.

TBR=smcgruer@chromium.org

Bug: 986925
Change-Id: I3a9a924ce15f05aa30588004d815fdfa9d60ded1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1714153
Commit-Queue: Yi Gu <yigu@chromium.org>
Reviewed-by: Majid Valipour <majidvp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#680189}

third_party/blink/renderer/core/animation/animation_effect.cc

@@ -88,9 +88,6 @@ void AnimationEffect::UpdateInheritedTime(double inherited_time,
   double time_to_next_iteration = std::numeric_limits<double>::infinity();
   if (needs_update) {
     const double active_duration = SpecifiedTiming().ActiveDuration();
-    // TODO(yigu): Direction of WorkletAnimation is always forwards based on
-    // the calculation. Need to unify the logic to handle it correctly.
-    // https://crbug.com/896249.
     const AnimationDirection direction =
         (GetAnimation() && GetAnimation()->playbackRate() < 0) ? kBackwards
                                                                : kForwards;

third_party/blink/renderer/modules/animationworklet/worklet_animation.cc

@@ -692,6 +692,10 @@ bool WorkletAnimation::IsCurrentTimeInitialized() const {
 //
 // Changing scroll-linked animation start_time initialization is under
 // consideration here: https://github.com/w3c/csswg-drafts/issues/2075.
+//
+// TODO(https://crbug.com/986925): The playback rate should be taken into
+// consideration when calculating the initial current time.
+// https://drafts.csswg.org/web-animations/#playing-an-animation-section
 base::Optional<base::TimeDelta> WorkletAnimation::InitialCurrentTime() const {
   if (play_state_ == Animation::kIdle || play_state_ == Animation::kUnset ||
       !IsTimelineActive())