Attempt to fix the crash in blink Scroll Animator.

third_party/WebKit/Source/platform/scroll/ScrollableArea.cpp

Index: third_party/WebKit/Source/platform/scroll/ScrollableArea.cpp
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollableArea.cpp b/third_party/WebKit/Source/platform/scroll/ScrollableArea.cpp
index f91bc0ff01e9bbcd0b41e2c11f60264744ee9243..8ab050ed1c1bb8afa4729f5dff72104817507529 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollableArea.cpp
+++ b/third_party/WebKit/Source/platform/scroll/ScrollableArea.cpp
@@ -94,7 +94,7 @@ ScrollableArea::~ScrollableArea()
 
 void ScrollableArea::clearScrollAnimators()
 {
-#if OS(MACOSX) && ENABLE(OILPAN)

[ajuma, 2016/02/22 15:15:01]

Instead of using an #if, WDYT of adding a virtual method that has an empty
implementation in ScrollAnimatorCompositorCoordinator and whose implementation
in ScrollAnimatorMac calls dispose()?

[bokan, 2016/02/22 15:55:35]

Why do we need to manually call dispose here at all? The animator is GCd so
can't we just clear the pointer and let Oilpan call dispose when the time is
right?

If there's something else that we need to happen *right here* (e.g. I see
ScrollAnimatorMac invalidates some painting code) then we should be doing that
through a method other than dispose.

[ymalik, 2016/02/22 19:22:56]

I think they have this call here because if oilpan is not enabled, dispose would
be called by the destructor, but if oilpan is enabled, presumably we want to
"dispose" right when ~ScrollableArea is called and not wait for dispose to be
called by oilpan (this function is called by ~ScrollableArea).  

[bokan, 2016/02/22 19:35:46]

The only place I see this being called from is
PaintLayerScrollableArea::dispose(). With Oilpan on, destructors aren't called
at all IIRC. If we have something here that needs to happen at a specific
time/order, we shouldn't put it in the dispose method. Otherwise, just let
Oilpan handle it.

+#if ENABLE(OILPAN)
     if (m_scrollAnimator)
         m_scrollAnimator->dispose();
 #endif