Declare onFinish event handler for AnimationPlayer

Source/core/animation/DocumentTimeline.cpp

 /*
  * 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 61 matching lines @@
 {
     RefPtr<AnimationPlayer> player = AnimationPlayer::create(*this, child);
     AnimationPlayer* result = player.get();
     m_players.add(result);
     setOutdatedAnimationPlayer(result);
     return result;
 }
 
 AnimationPlayer* DocumentTimeline::play(TimedItem* child)
 {
+    if (!m_document)
+        return 0;
     AnimationPlayer* player = createAnimationPlayer(child);
     player->setStartTime(effectiveTime());
     return player;
 }
 
 void DocumentTimeline::wake()
 {
     m_timing->serviceOnNextFrame();
 }
 
@@ skipping 91 matching lines @@
     size_t count = 0;
     for (HashSet<RefPtr<AnimationPlayer> >::iterator it = m_playersNeedingUpdate.begin(); it != m_playersNeedingUpdate.end(); ++it) {
         const TimedItem* timedItem = (*it)->source();
         if ((*it)->hasStartTime())
             count += (timedItem && (timedItem->isCurrent() || timedItem->isInEffect()));
     }
     return count;
 }
 
 void DocumentTimeline::detachFromDocument() {
+    // FIXME: DocumentTimeline should keep Document alive.
     m_document = 0;
 }
 
 } // namespace