Initial implementation of AudioTrack, AudioTrackList, VideoTrack, and VideoTrackList.

Source/core/html/track/TrackBase.cpp

Index: Source/core/html/track/TrackBase.cpp
diff --git a/Source/core/html/track/TrackBase.cpp b/Source/core/html/track/TrackBase.cpp
index a11c065f41080f3d1d9d5b8d9e5b8b5c4a43105d..804652ee3465ce1459c8ee9faac83e12d08e3672 100644
--- a/Source/core/html/track/TrackBase.cpp
+++ b/Source/core/html/track/TrackBase.cpp
@@ -38,11 +38,13 @@ TrackBase::TrackBase(Type type, const AtomicString& label, const AtomicString& l
     , m_label(label)
     , m_language(language)
     , m_id(id)
+    , m_mediaElement(0)
 {
 }
 
 TrackBase::~TrackBase()
 {
+    ASSERT(!m_mediaElement);
 }
 
 void TrackBase::setKind(const AtomicString& kind)
@@ -54,4 +56,3 @@ void TrackBase::setKind(const AtomicString& kind)
 }
 
 } // namespace WebCore
-