Attempt to fix the crash in blink Scroll Animator.

third_party/WebKit/Source/platform/scroll/ScrollAnimatorBase.h

 /*
  * Copyright (c) 2010, 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 36 matching lines @@
 class Scrollbar;
 
 class PLATFORM_EXPORT ScrollAnimatorBase : public ScrollAnimatorCompositorCoordinator {
 public:
     static PassOwnPtrWillBeRawPtr<ScrollAnimatorBase> create(ScrollableArea*);
 
     virtual ~ScrollAnimatorBase();
 
     virtual void dispose() { }
 
+    virtual void clearScrollAnimator() { return ScrollAnimatorCompositorCoordinator::dispose(); }
+
     // Computes a scroll destination for the given parameters.  The returned
     // ScrollResultOneDimensional will have didScroll set to false if already at
     // the destination.  Otherwise, starts scrolling towards the destination and
     // didScroll is true.  Scrolling may be immediate or animated. The base
     // class implementation always scrolls immediately, never animates.
     virtual ScrollResultOneDimensional userScroll(ScrollbarOrientation, ScrollGranularity, float step, float delta);
 
     virtual void scrollToOffsetWithoutAnimation(const FloatPoint&);
 
 #if OS(MACOSX)
@@ skipping 54 matching lines @@
     float clampScrollPosition(ScrollbarOrientation, float) const;
 
     RawPtrWillBeMember<ScrollableArea> m_scrollableArea;
     float m_currentPosX; // We avoid using a FloatPoint in order to reduce
     float m_currentPosY; // subclass code complexity.
 };
 
 } // namespace blink
 
 #endif // ScrollAnimatorBase_h