Oilpan: add transition types to track interface objects.

Source/core/html/track/TextTrackCue.cpp

Index: Source/core/html/track/TextTrackCue.cpp
diff --git a/Source/core/html/track/TextTrackCue.cpp b/Source/core/html/track/TextTrackCue.cpp
index ebf262f9b282d4d7db3b120dd822398f4e87a550..8a57afeba54c55b101342012c6a2e42dd81eed35 100644
--- a/Source/core/html/track/TextTrackCue.cpp
+++ b/Source/core/html/track/TextTrackCue.cpp
@@ -55,7 +55,7 @@ TextTrackCue::TextTrackCue(double start, double end)
     : m_startTime(start)
     , m_endTime(end)
     , m_cueIndex(invalidCueIndex)
-    , m_track(0)
+    , m_track(nullptr)
     , m_isActive(false)
     , m_pauseOnExit(false)
 {
@@ -174,4 +174,9 @@ const AtomicString& TextTrackCue::interfaceName() const
     return EventTargetNames::TextTrackCue;
 }
 
+void TextTrackCue::trace(Visitor* visitor)
+{
+    visitor->trace(m_track);
+}
+
 } // namespace WebCore