Attempt to fix the crash in blink Scroll Animator.

third_party/WebKit/Source/platform/mac/ScrollAnimatorMac.h

 /*
  * Copyright (C) 2010, 2011 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 33 matching lines @@
 
 class Scrollbar;
 
 class PLATFORM_EXPORT ScrollAnimatorMac : public ScrollAnimatorBase {
     WILL_BE_USING_PRE_FINALIZER(ScrollAnimatorMac, dispose);
 public:
     ScrollAnimatorMac(ScrollableArea*);
     ~ScrollAnimatorMac() override;
 
     void dispose() override;
+    void clearScrollAnimator() override;
 
     void immediateScrollToPointForScrollAnimation(const FloatPoint& newPosition);
     bool haveScrolledSincePageLoad() const { return m_haveScrolledSincePageLoad; }
 
     void updateScrollerStyle();
 
     bool scrollbarPaintTimerIsActive() const;
     void startScrollbarPaintTimer();
     void stopScrollbarPaintTimer();
 
@@ skipping 64 matching lines @@
     void immediateScrollTo(const FloatPoint&);
 
     bool m_haveScrolledSincePageLoad;
     bool m_needsScrollerStyleUpdate;
     IntRect m_visibleScrollerThumbRect;
 };
 
 } // namespace blink
 
 #endif // ScrollAnimatorMac_h