Have Player take the DocumentTimeline object by reference

Source/core/animation/Player.h

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 24 matching lines @@
 #include "wtf/RefPtr.h"
 
 namespace WebCore {
 
 class DocumentTimeline;
 
 class Player FINAL : public RefCounted<Player> {
 
 public:
     ~Player();
-    static PassRefPtr<Player> create(DocumentTimeline*, TimedItem*);
+    static PassRefPtr<Player> create(DocumentTimeline&, TimedItem*);
 
     // Returns whether this player is still current or in effect.
     // timeToEffectChange returns:
     //  infinity  - if this player is no longer in effect
     //  0         - if this player requires an update on the next frame
     //  n         - if this player requires an update after 'n' units of time
     bool update(double* timeToEffectChange = 0);
 
     void cancel();
     double currentTime() const;
     void setCurrentTime(double);
     bool paused() const { return !m_isPausedForTesting && pausedInternal(); }
     void setPaused(bool);
     double playbackRate() const { return m_playbackRate; }
     void setPlaybackRate(double);
     double startTime() const { return m_startTime; }
     double timeDrift() const;
-    DocumentTimeline* timeline() { return m_timeline; }
+    DocumentTimeline& timeline() { return m_timeline; }
     TimedItem* source() { return m_content.get(); }
 
     // Pausing via this method is not reflected in the value returned by
     // paused() and must never overlap with pausing via setPaused().
     void pauseForTesting();
     // Reflects all pausing, including via pauseForTesting().
     bool pausedInternal() const { return !isNull(m_pauseStartTime); }
 
 private:
-    Player(DocumentTimeline*, TimedItem*);
+    Player(DocumentTimeline&, TimedItem*);
     static double effectiveTime(double time) { return isNull(time) ? 0 : time; }
     inline double pausedTimeDrift() const;
     inline double currentTimeBeforeDrift() const;
 
     void setPausedImpl(bool);
 
     double m_pauseStartTime;
     double m_playbackRate;
     double m_timeDrift;
     const double m_startTime;
 
     RefPtr<TimedItem> m_content;
-    DocumentTimeline* const m_timeline;
+    DocumentTimeline& m_timeline;
     bool m_isPausedForTesting;
 };
 
 } // namespace
 
 #endif