Attempt to fix the crash in blink Scroll Animator.

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

 /*
  * 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 674 matching lines @@
 ScrollAnimatorMac::ScrollAnimatorMac(ScrollableArea* scrollableArea)
     : ScrollAnimatorBase(scrollableArea)
     , m_initialScrollbarPaintTimer(this, &ScrollAnimatorMac::initialScrollbarPaintTimerFired)
     , m_sendContentAreaScrolledTimer(this, &ScrollAnimatorMac::sendContentAreaScrolledTimerFired)
     , m_haveScrolledSincePageLoad(false)
     , m_needsScrollerStyleUpdate(false)
 {
 #if ENABLE(OILPAN)
     ThreadState::current()->registerPreFinalizer(this);
 #endif
-
     m_scrollAnimationHelperDelegate.adoptNS([[BlinkScrollAnimationHelperDelegate alloc] initWithScrollAnimator:this]);
     m_scrollAnimationHelper.adoptNS([[NSClassFromString(@"NSScrollAnimationHelper") alloc] initWithDelegate:m_scrollAnimationHelperDelegate.get()]);
 
     if (ScrollbarThemeMacCommon::isOverlayAPIAvailable()) {
         m_scrollbarPainterControllerDelegate.adoptNS([[BlinkScrollbarPainterControllerDelegate alloc] initWithScrollableArea:scrollableArea]);
         m_scrollbarPainterController = [[[NSClassFromString(@"NSScrollerImpPair") alloc] init] autorelease];
         [m_scrollbarPainterController.get() performSelector:@selector(setDelegate:) withObject:m_scrollbarPainterControllerDelegate.get()];
         [m_scrollbarPainterController.get() setScrollerStyle:ScrollbarThemeMacCommon::recommendedScrollerStyle()];
     }
 }
@@ skipping 13 matching lines @@
         [m_scrollbarPainterController.get() setDelegate:nil];
         [m_horizontalScrollbarPainterDelegate.get() invalidate];
         [m_verticalScrollbarPainterDelegate.get() invalidate];
         [m_scrollAnimationHelperDelegate.get() invalidate];
         END_BLOCK_OBJC_EXCEPTIONS;
     }
     m_initialScrollbarPaintTimer.stop();
     m_sendContentAreaScrolledTimer.stop();
 }
 
+void ScrollAnimatorMac::clearScrollAnimator()
+{
+    dispose();
+    ScrollAnimatorBase::dispose();
+}
+
 ScrollResultOneDimensional ScrollAnimatorMac::userScroll(ScrollbarOrientation orientation, ScrollGranularity granularity, float step, float delta)
 {
     m_haveScrolledSincePageLoad = true;
 
     if (!m_scrollableArea->scrollAnimatorEnabled())
         return ScrollAnimatorBase::userScroll(orientation, granularity, step, delta);
 
     if (granularity == ScrollByPixel || granularity == ScrollByPrecisePixel)
         return ScrollAnimatorBase::userScroll(orientation, granularity, step, delta);
 
@@ skipping 439 matching lines @@
         return;
 
     m_visibleScrollerThumbRect = rectInViewCoordinates;
 }
 
 bool ScrollAnimatorMac::canUseCoordinatedScrollbar() {
     return ScrollbarThemeMacCommon::isOverlayAPIAvailable();
 }
 
 } // namespace blink