Oilpan: trace RenderVTTCue's cue back reference.

Source/core/rendering/RenderVTTCue.cpp

 /*
  * Copyright (C) 2012 Victor Carbune (victor@rosedu.org)
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 19 matching lines @@
 #include "core/rendering/RenderView.h"
 
 namespace blink {
 
 RenderVTTCue::RenderVTTCue(VTTCueBox* element)
     : RenderBlockFlow(element)
     , m_cue(element->getCue())
 {
 }
 
+void RenderVTTCue::trace(Visitor* visitor)
+{
+    visitor->trace(m_cue);
+    RenderBlockFlow::trace(visitor);
+}
+
 void RenderVTTCue::layout()
 {
     RenderBlockFlow::layout();
 
     // If WebVTT Regions are used, the regular WebVTT layout algorithm is no
     // longer necessary, since cues having the region parameter set do not have
     // any positioning parameters. Also, in this case, the regions themselves
     // have positioning information.
     if (!m_cue->regionId().isEmpty())
         return;
@@ skipping 210 matching lines @@
     }
 }
 
 void RenderVTTCue::repositionCueSnapToLinesNotSet()
 {
     // FIXME: Implement overlapping detection when snap-to-lines is not set. http://wkb.ug/84296
 }
 
 } // namespace blink