Implement DataCue interface.

Source/core/html/track/TextTrackCue.h

Index: Source/core/html/track/TextTrackCue.h
diff --git a/Source/core/html/track/TextTrackCue.h b/Source/core/html/track/TextTrackCue.h
index dd2d235b732a6c29dd45650f127c376b880e9d0b..3a0cf727e18a7e7895b8714a0b20a67243b8ff10 100644
--- a/Source/core/html/track/TextTrackCue.h
+++ b/Source/core/html/track/TextTrackCue.h
@@ -79,13 +79,16 @@ public:
     bool isActive();
     void setIsActive(bool);
 
-    virtual void updateDisplay(const IntSize& videoSize, HTMLDivElement& container) = 0;
+    virtual void updateDisplay(const IntSize& videoSize, HTMLDivElement& container) { };
 
     // FIXME: Consider refactoring to eliminate or merge the following three members.
     // https://code.google.com/p/chromium/issues/detail?id=322434
-    virtual void updateDisplayTree(double movieTime) = 0;
-    virtual void removeDisplayTree() = 0;
-    virtual void notifyRegionWhenRemovingDisplayTree(bool notifyRegion) = 0;
+    virtual void updateDisplayTree(double movieTime) { };
+    virtual void removeDisplayTree() { };
+    virtual void notifyRegionWhenRemovingDisplayTree(bool notifyRegion) { };
+
+    enum CueType { WebVTT, Data };
+    virtual CueType cueType() const = 0;
 
     virtual const AtomicString& interfaceName() const OVERRIDE;