Web Animations: Use null for unresolved startTime and currentTime in AnimationPlayer

Source/core/animation/AnimationPlayer.cpp

Index: Source/core/animation/AnimationPlayer.cpp
diff --git a/Source/core/animation/AnimationPlayer.cpp b/Source/core/animation/AnimationPlayer.cpp
index 6d4e287345dd835980d56907164d16d1f4faa32a..97f5b92eef45111fc7deb227386a16dc822ae98c 100644
--- a/Source/core/animation/AnimationPlayer.cpp
+++ b/Source/core/animation/AnimationPlayer.cpp
@@ -147,11 +147,25 @@ void AnimationPlayer::updateCurrentTimingState(TimingUpdateReason reason)
     m_holdTime = m_playbackRate < 0 ? 0 : sourceEnd();
 }
 
+double AnimationPlayer::startTime(bool& isNull) const
+{
+    double result = startTime();
+    isNull = std::isnan(result);
+    return result;
+}
+
 double AnimationPlayer::startTime() const
 {
     return m_startTime * 1000;
 }
 
+double AnimationPlayer::currentTime(bool& isNull)
+{
+    double result = currentTime();
+    isNull = std::isnan(result);
+    return result;
+}
+
 double AnimationPlayer::currentTime()
 {
     if (m_currentTimePending || m_idle)