Remove TextTrackClient interface to simplify TextTrack code.

Source/core/html/track/InbandTextTrack.h

Index: Source/core/html/track/InbandTextTrack.h
diff --git a/Source/core/html/track/InbandTextTrack.h b/Source/core/html/track/InbandTextTrack.h
index df3c7d7240e549672629b5f63ce5b0c147f2a7c7..268340ab194118a0208fc9b21b0a5937eed7ca0b 100644
--- a/Source/core/html/track/InbandTextTrack.h
+++ b/Source/core/html/track/InbandTextTrack.h
@@ -43,14 +43,14 @@ class TextTrackCue;
 
 class InbandTextTrack FINAL : public TextTrack, public blink::WebInbandTextTrackClient {
 public:
-    static PassRefPtr<InbandTextTrack> create(Document&, TextTrackClient*, blink::WebInbandTextTrack*);
+    static PassRefPtr<InbandTextTrack> create(Document&, blink::WebInbandTextTrack*);
     virtual ~InbandTextTrack();
 
     size_t inbandTrackIndex();
     virtual void setTrackList(TextTrackList*) OVERRIDE FINAL;
 
 private:
-    InbandTextTrack(Document&, TextTrackClient*, blink::WebInbandTextTrack*);
+    InbandTextTrack(Document&, blink::WebInbandTextTrack*);
 
     virtual void addWebVTTCue(double, double, const blink::WebString&, const blink::WebString&, const blink::WebString&) OVERRIDE;