Add AnimationTimeDelta::operator/(T), as well as /=.

It already had *, and the underlying TimeDelta has long had /(T), so
this just makes the API a little less asymmetric.

This simplifies one callsite.

Bug: none
Change-Id: I49fe5f69a36c53c7857e623f17f7c5b4e66346f4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2344815
Auto-Submit: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Kevin Ellis <kevers@chromium.org>
Reviewed-by: Kevin Ellis <kevers@chromium.org>
Cr-Commit-Position: refs/heads/master@{#796369}

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

@@ -1936,16 +1936,15 @@ base::Optional<AnimationTimeDelta> Animation::TimeToEffectChange() {
                                             playback_rate_);
   }
 
-  double result =
+  AnimationTimeDelta result =
       playback_rate_ > 0
-          ? content_->TimeToForwardsEffectChange().InSecondsF() / playback_rate_
-          : content_->TimeToReverseEffectChange().InSecondsF() /
-                -playback_rate_;
+          ? content_->TimeToForwardsEffectChange() / playback_rate_
+          : content_->TimeToReverseEffectChange() / -playback_rate_;
 
   return !HasActiveAnimationsOnCompositor() &&
                  content_->GetPhase() == Timing::kPhaseActive
              ? AnimationTimeDelta()
-             : AnimationTimeDelta::FromSecondsD(result);
+             : result;
 }
 
 void Animation::cancel() {

third_party/blink/renderer/core/animation/animation_time_delta.h

@@ -80,6 +80,14 @@ class CORE_EXPORT AnimationTimeDelta {
   AnimationTimeDelta& operator*=(V a) {
     return *this = (*this * a);
   }
+  template <typename T>
+  AnimationTimeDelta operator/(T a) const {
+    return AnimationTimeDelta(delta_ / a);
+  }
+  template <typename T>
+  AnimationTimeDelta& operator/=(T a) {
+    return *this = (*this / a);
+  }
 
  protected:
   constexpr explicit AnimationTimeDelta(double delta) : delta_(delta) {}