Implement AudioTrack, AudioTrackList, VideoTrack, and VideoTrackList

Source/bindings/v8/custom/V8TrackEventCustom.cpp

Index: Source/bindings/v8/custom/V8TrackEventCustom.cpp
diff --git a/Source/bindings/v8/custom/V8TrackEventCustom.cpp b/Source/bindings/v8/custom/V8TrackEventCustom.cpp
index 29d05799634706ee356429544d746394956f1048..9c2b04e3c31863545e3f3edee7a028b9b11c79ca 100644
--- a/Source/bindings/v8/custom/V8TrackEventCustom.cpp
+++ b/Source/bindings/v8/custom/V8TrackEventCustom.cpp
@@ -31,7 +31,9 @@
 #include "config.h"
 #include "bindings/core/v8/V8TrackEvent.h"
 
+#include "bindings/core/v8/V8AudioTrack.h"
 #include "bindings/core/v8/V8TextTrack.h"
+#include "bindings/core/v8/V8VideoTrack.h"
 #include "core/html/track/TrackBase.h"
 #include "core/html/track/TrackEvent.h"
 
@@ -53,10 +55,12 @@ void V8TrackEvent::trackAttributeGetterCustom(const v8::PropertyCallbackInfo<v8:
         return;
 
     case TrackBase::AudioTrack:
+        v8SetReturnValueFast(info, static_cast<AudioTrack*>(track), trackEvent);
+        return;
+
     case TrackBase::VideoTrack:
-        // This should not happen until VideoTrack and AudioTrack are implemented.
-        ASSERT_NOT_REACHED();
-        break;
+        v8SetReturnValueFast(info, static_cast<VideoTrack*>(track), trackEvent);
+        return;
     }
 
     v8SetReturnValueNull(info);