Oilpan: add transition types to track interface objects.

Source/core/html/track/vtt/VTTRegion.cpp

Index: Source/core/html/track/vtt/VTTRegion.cpp
diff --git a/Source/core/html/track/vtt/VTTRegion.cpp b/Source/core/html/track/vtt/VTTRegion.cpp
index bea2d7957b256dea83f40aac3b5235829ccefd91..c67428a0c25a9af10d2c7fb9df3d20f10659425c 100644
--- a/Source/core/html/track/vtt/VTTRegion.cpp
+++ b/Source/core/html/track/vtt/VTTRegion.cpp
@@ -88,7 +88,7 @@ VTTRegion::VTTRegion()
     , m_regionAnchor(FloatPoint(defaultAnchorPointX, defaultAnchorPointY))
     , m_viewportAnchor(FloatPoint(defaultAnchorPointX, defaultAnchorPointY))
     , m_scroll(defaultScroll)
-    , m_track(0)
+    , m_track(nullptr)
     , m_currentTop(0)
     , m_scrollTimer(this, &VTTRegion::scrollTimerFired)
 {
@@ -471,4 +471,9 @@ void VTTRegion::scrollTimerFired(Timer<VTTRegion>*)
     displayLastVTTCueBox();
 }
 
+void VTTRegion::trace(Visitor* visitor)
+{
+    visitor->trace(m_track);
+}
+
 } // namespace WebCore