Web Animations: Fix CSS events to handle animations with very short durations

Source/core/animation/TimedItem.h

Index: Source/core/animation/TimedItem.h
diff --git a/Source/core/animation/TimedItem.h b/Source/core/animation/TimedItem.h
index 93b79a7fc7b9503257f36bbed398dab0249c2b72..501a71170224154f1a2230bacd501a110f04793e 100644
--- a/Source/core/animation/TimedItem.h
+++ b/Source/core/animation/TimedItem.h
@@ -49,17 +49,26 @@ static inline double nullValue()
     return std::numeric_limits<double>::quiet_NaN();
 }
 
-class TimedItemEventDelegate {
-public:
-    virtual ~TimedItemEventDelegate() { };
-    virtual void onEventCondition(bool wasInPlay, bool isInPlay, double previousIteration, double currentIteration) = 0;
-};
-
 class TimedItem : public RefCounted<TimedItem> {
     friend class Player; // Calls attach/detach, updateInheritedTime.
 public:
+    // Note that logic in CSSAnimations depends on the order of these values.
+    enum Phase {
+        PhaseBefore,
+        PhaseActive,
+        PhaseAfter,
+        PhaseNone,
+    };
+
+    class EventDelegate {
+    public:
+        virtual ~EventDelegate() { };
+        virtual void onEventCondition(bool isFirstSample, Phase previousPhase, Phase currentPhase, double previousIteration, double currentIteration) = 0;
+    };
+
     virtual ~TimedItem() { }
 
+    Phase phase() const { return ensureCalculated().phase; }
     bool isCurrent() const { return ensureCalculated().isCurrent; }
     bool isInEffect() const { return ensureCalculated().isInEffect; }
     bool isInPlay() const { return ensureCalculated().isInPlay; }
@@ -71,15 +80,8 @@ public:
     double timeFraction() const { return ensureCalculated().timeFraction; }
     Player* player() const { return m_player; }
 
-    enum Phase {
-        PhaseBefore,
-        PhaseActive,
-        PhaseAfter,
-        PhaseNone,
-    };
-
 protected:
-    TimedItem(const Timing&, PassOwnPtr<TimedItemEventDelegate> = nullptr);
+    TimedItem(const Timing&, PassOwnPtr<EventDelegate> = nullptr);
 
     // When TimedItem receives a new inherited time via updateInheritedTime
     // it will (if necessary) recalculate timings and (if necessary) call
@@ -103,18 +105,19 @@ private:
     const double m_startTime;
     Player* m_player;
     Timing m_specified;
-    OwnPtr<TimedItemEventDelegate> m_eventDelegate;
+    OwnPtr<EventDelegate> m_eventDelegate;
 
     // FIXME: Should be versioned by monotonic value on player.
     mutable struct CalculatedTiming {
-        CalculatedTiming();
         double activeDuration;
+        Phase phase;
         double currentIteration;
         double timeFraction;
         bool isCurrent;
         bool isInEffect;
         bool isInPlay;
     } m_calculated;
+    mutable bool m_isFirstSample;
 
     // FIXME: Should check the version and reinherit time if inconsistent.
     const CalculatedTiming& ensureCalculated() const { return m_calculated; }