Remove TextTrackClient interface to simplify TextTrack code.

Source/core/html/HTMLTrackElement.h

Index: Source/core/html/HTMLTrackElement.h
diff --git a/Source/core/html/HTMLTrackElement.h b/Source/core/html/HTMLTrackElement.h
index 68c00eb7e455a60b89400ebc6bd5d791c4e66ed7..11406a7b8a4aba9ff416f317864582906dd2eb38 100644
--- a/Source/core/html/HTMLTrackElement.h
+++ b/Source/core/html/HTMLTrackElement.h
@@ -34,7 +34,7 @@ namespace WebCore {
 
 class HTMLMediaElement;
 
-class HTMLTrackElement FINAL : public HTMLElement, public TextTrackClient {
+class HTMLTrackElement FINAL : public HTMLElement {
 public:
     static PassRefPtr<HTMLTrackElement> create(Document&);
 
@@ -69,14 +69,6 @@ private:
 
     HTMLMediaElement* mediaElement() const;
 
-    // TextTrackClient
-    virtual void textTrackModeChanged(TextTrack*) OVERRIDE;
-    virtual void textTrackKindChanged(TextTrack*) OVERRIDE;
-    virtual void textTrackAddCues(TextTrack*, const TextTrackCueList*) OVERRIDE;
-    virtual void textTrackRemoveCues(TextTrack*, const TextTrackCueList*) OVERRIDE;
-    virtual void textTrackAddCue(TextTrack*, PassRefPtr<TextTrackCue>) OVERRIDE;
-    virtual void textTrackRemoveCue(TextTrack*, PassRefPtr<TextTrackCue>) OVERRIDE;
-
     LoadableTextTrack* ensureTrack();
     bool canLoadUrl(const KURL&);