Oilpan: add missing leftmost trace()s for GC mixins.

Source/core/html/track/VideoTrack.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "core/html/track/VideoTrack.h"
 
 #include "core/html/HTMLMediaElement.h"
 
 namespace blink {
 
 VideoTrack::VideoTrack(const String& id, const AtomicString& kind, const AtomicString& label, const AtomicString& language, bool selected)
     : TrackBase(TrackBase::VideoTrack, label, language, id)
     , m_selected(selected)
 {
     setKind(kind);
 }
 
 VideoTrack::~VideoTrack()
 {
 }
 
+void VideoTrack::trace(Visitor* visitor)
+{
+    TrackBase::trace(visitor);
+}
+
 void VideoTrack::setSelected(bool selected)
 {
     if (selected == m_selected)
         return;
 
     m_selected = selected;
 
     if (mediaElement()) {
         blink::WebMediaPlayer::TrackId selectedTrackId = trackId();
         mediaElement()->selectedVideoTrackChanged(selected ? &selectedTrackId : 0);
@@ skipping 46 matching lines @@
         || (kind == commentaryKeyword())
         || (kind == emptyAtom);
 }
 
 AtomicString VideoTrack::defaultKind() const
 {
     return emptyAtom;
 }
 
 }