Attempt to fix the crash in blink Scroll Animator.

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

Index: third_party/WebKit/Source/platform/mac/ScrollAnimatorMac.mm
diff --git a/third_party/WebKit/Source/platform/mac/ScrollAnimatorMac.mm b/third_party/WebKit/Source/platform/mac/ScrollAnimatorMac.mm
index 6f940cb75decad84a1bb1ab2c93ed210adf89f45..3dbe2cfeabf75e6da2d935b756d9c40363b8ee41 100644
--- a/third_party/WebKit/Source/platform/mac/ScrollAnimatorMac.mm
+++ b/third_party/WebKit/Source/platform/mac/ScrollAnimatorMac.mm
@@ -692,7 +692,6 @@ ScrollAnimatorMac::ScrollAnimatorMac(ScrollableArea* scrollableArea)
 #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()]);
 
@@ -726,6 +725,12 @@ void ScrollAnimatorMac::dispose()
     m_sendContentAreaScrolledTimer.stop();
 }
 
+void ScrollAnimatorMac::clearScrollAnimator()
+{
+    dispose();
+    ScrollAnimatorBase::dispose();
+}
+
 ScrollResultOneDimensional ScrollAnimatorMac::userScroll(ScrollbarOrientation orientation, ScrollGranularity granularity, float step, float delta)
 {
     m_haveScrolledSincePageLoad = true;