Unregister AnimationPlayer from ActiveDOMObjects on timeline deletion.

Source/core/animation/AnimationPlayer.cpp

Index: Source/core/animation/AnimationPlayer.cpp
diff --git a/Source/core/animation/AnimationPlayer.cpp b/Source/core/animation/AnimationPlayer.cpp
index 30c585ede03a36c0ed1fe710c3e0f3d292e717ae..d4ab95818633143d4272cd91a17c128be193d262 100644
--- a/Source/core/animation/AnimationPlayer.cpp
+++ b/Source/core/animation/AnimationPlayer.cpp
@@ -712,6 +712,8 @@ void AnimationPlayer::setCompositorPending(bool sourceChanged)
         || !playing() || m_compositorState->playbackRate != m_playbackRate
         || m_compositorState->startTime != m_startTime) {
         m_compositorPending = true;
+        ASSERT(timeline());
+        ASSERT(timeline()->document());
         timeline()->document()->compositorPendingAnimations().add(this);
     }
 }