Bug 1223658 - Part 4: Add a function to check active duration is zero. r=birtles,dholbert

We are going to pass animations to the compositor in before phase but not to
pass when active duration is zero.  To distinguish this state we need a new
function to check that the active duration is zero.

MozReview-Commit-ID: 2Lckmt4LQcV

--HG--
extra : rebase_source : aa059b8c75bcea4ff4c5788aac98d1e17a4a5d7b

dom/animation/AnimationEffectReadOnly.h

@@ -52,6 +52,10 @@ public:
   bool IsInPlay() const;
   bool IsCurrent() const;
   bool IsInEffect() const;
+  bool IsActiveDurationZero() const
+  {
+    return SpecifiedTiming().ActiveDuration() == StickyTimeDuration();
+  }
 
   already_AddRefed<AnimationEffectTimingReadOnly> Timing();
   const TimingParams& SpecifiedTiming() const