moebius#89: DOM - implement animationcancel event

Issue #55

layout/style/AnimationCommon.h

@@ -251,6 +251,26 @@ ImplCycleCollectionTraverse(nsCycleCollectionTraversalCallback& aCallback,
   aField.Traverse(&aCallback, aName);
 }
 
+// Return the TransitionPhase or AnimationPhase to use when the animation
+// doesn't have a target effect.
+template <typename PhaseType>
+PhaseType GetAnimationPhaseWithoutEffect(const dom::Animation& aAnimation)
+{
+  MOZ_ASSERT(!aAnimation.GetEffect(),
+             "Should only be called when we do not have an effect");
+
+  Nullable<TimeDuration> currentTime = aAnimation.GetCurrentTime();
+  if (currentTime.IsNull()) {
+    return PhaseType::Idle;
+  }
+
+  // If we don't have a target effect, the duration will be zero so the phase is
+  // 'before' if the current time is less than zero.
+  return currentTime.Value() < TimeDuration()
+         ? PhaseType::Before
+         : PhaseType::After;
+};
+
 } // namespace mozilla
 
 #endif /* !defined(mozilla_css_AnimationCommon_h) */