Move text track active list management to CueTimeline

Source/core/html/track/TextTrack.h

Index: Source/core/html/track/TextTrack.h
diff --git a/Source/core/html/track/TextTrack.h b/Source/core/html/track/TextTrack.h
index a99c260e4ca7660c7f2a115dd83261c30df007dc..aff0ed7191d6d4bdbc492e54f3722a016792b4b1 100644
--- a/Source/core/html/track/TextTrack.h
+++ b/Source/core/html/track/TextTrack.h
@@ -34,6 +34,7 @@
 
 namespace blink {
 
+class CueTimeline;
 class ExceptionState;
 class HTMLMediaElement;
 class TextTrack;
@@ -124,6 +125,8 @@ protected:
     virtual bool isValidKind(const AtomicString& kind) const override { return isValidKindKeyword(kind); }
     virtual AtomicString defaultKind() const override { return subtitlesKeyword(); }
 
+    CueTimeline* cueTimeline() const;
+
     RefPtrWillBeMember<TextTrackCueList> m_cues;
 
 private: