Safely finalize an AnimationTimeline's still-attached Animations.

third_party/WebKit/Source/core/animation/AnimationTimeline.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 54 matching lines @@
 }
 
 AnimationTimeline::AnimationTimeline(Document* document, PlatformTiming* timing)
     : m_document(document)
     , m_zeroTime(0) // 0 is used by unit tests which cannot initialize from the loader
     , m_zeroTimeInitialized(false)
     , m_outdatedAnimationCount(0)
     , m_playbackRate(1)
     , m_lastCurrentTimeInternal(0)
 {
+    ThreadState::current()->registerPreFinalizer(this);
     if (!timing)
         m_timing = new AnimationTimelineTiming(this);
     else
         m_timing = timing;
 
     if (RuntimeEnabledFeatures::compositorAnimationTimelinesEnabled() && Platform::current()->isThreadedAnimationEnabled()) {
         ASSERT(Platform::current()->compositorSupport());
         m_compositorTimeline = adoptPtr(Platform::current()->compositorSupport()->createAnimationTimeline());
     }
 
     ASSERT(document);
 }
 
 AnimationTimeline::~AnimationTimeline()
 {
 }
 
+void AnimationTimeline::dispose()
+{
+    // The Animation objects depend on using this AnimationTimeline to
+    // unregister from its underlying compositor timeline. To arrange
+    // for that safely, this dispose() method will return first
+    // during prefinalization, notifying each Animation object of
+    // impending destruction.
+    for (const auto& animation : m_animations)
+        animation->dispose();
+}
+
 bool AnimationTimeline::isActive()
 {
     return m_document && m_document->page();
 }
 
 void AnimationTimeline::animationAttached(Animation& animation)
 {
     ASSERT(animation.timeline() == this);
     ASSERT(!m_animations.contains(&animation));
     m_animations.add(&animation);
@@ skipping 244 matching lines @@
 
 DEFINE_TRACE(AnimationTimeline)
 {
     visitor->trace(m_document);
     visitor->trace(m_timing);
     visitor->trace(m_animationsNeedingUpdate);
     visitor->trace(m_animations);
 }
 
 } // namespace