Drop [TypeChecking=Nullable]; deduce from attribute type instead

Source/core/animation/AnimationPlayer.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 85 matching lines @@
 #endif
 
     bool hasStartTime() const { return !isNull(m_startTime); }
     double startTime() const { return m_startTime * 1000; }
     double startTimeInternal() const { return m_startTime; }
     void setStartTime(double startTime) { setStartTimeInternal(startTime / 1000); }
     void setStartTimeInternal(double, bool isUpdateFromCompositor = false);
 
     const AnimationNode* source() const { return m_content.get(); }
     AnimationNode* source() { return m_content.get(); }
-    AnimationNode* source(bool& isNull) { isNull = !m_content; return m_content.get(); }
     void setSource(AnimationNode*);
 
     double timeLag() { return timeLagInternal() * 1000; }
     double timeLagInternal() { return currentTimeWithoutLag() - currentTimeInternal(); }
 
     // Pausing via this method is not reflected in the value returned by
     // paused() and must never overlap with pausing via pause().
     void pauseForTesting(double pauseTime);
     // This should only be used for CSS
     void unpause();
@@ skipping 69 matching lines @@
     bool m_finished;
     // Holds a 'finished' event queued for asynchronous dispatch via the
     // ScriptedAnimationController. This object remains active until the
     // event is actually dispatched.
     RefPtrWillBeMember<Event> m_pendingFinishedEvent;
 };
 
 } // namespace
 
 #endif