Move VTT functionality from TextTrackCue.* to VTTCue.*

Source/core/html/HTMLMediaElement.h

Index: Source/core/html/HTMLMediaElement.h
diff --git a/Source/core/html/HTMLMediaElement.h b/Source/core/html/HTMLMediaElement.h
index 9164199348bc7951c216e0f9adcb3ccc1a858b01..37da1fb3005428cc15784aeb8c90076b5c25d5f2 100644
--- a/Source/core/html/HTMLMediaElement.h
+++ b/Source/core/html/HTMLMediaElement.h
@@ -32,6 +32,7 @@
 #include "core/html/MediaControllerInterface.h"
 #include "core/html/track/TextTrack.h"
 #include "core/html/track/TextTrackCue.h"
+#include "core/html/track/vtt/VTTCue.h"
 #include "platform/PODIntervalTree.h"
 #include "platform/graphics/media/MediaPlayer.h"
 #include "public/platform/WebMimeRegistry.h"
@@ -581,7 +582,11 @@ template <>
 struct ValueToString<TextTrackCue*> {
     static String string(TextTrackCue* const& cue)
     {
-        return String::format("%p id=%s interval=%f-->%f cue=%s)", cue, cue->id().utf8().data(), cue->startTime(), cue->endTime(), cue->text().utf8().data());
+        if (cue->isVTTCue()) {
+            VTTCue* vttCue = toVTTCue(cue);
+            return String::format("%p id=%s interval=%f-->%f cue=%s)", cue, cue->id().utf8().data(), cue->startTime(), cue->endTime(), vttCue->text().utf8().data());
+        }
+        return String::format("%p id=%s interval=%f-->%f)", cue, cue->id().utf8().data(), cue->startTime(), cue->endTime());
     }
 };
 #endif