Oilpan: improve ScrollableArea handling.

Source/platform/scroll/ScrollAnimator.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 18 matching lines @@
  */
 
 #ifndef ScrollAnimator_h
 #define ScrollAnimator_h
 
 #include "platform/PlatformExport.h"
 #include "platform/PlatformWheelEvent.h"
 #include "platform/geometry/FloatSize.h"
 #include "platform/scroll/ScrollTypes.h"
 #include "wtf/Forward.h"
-#include "wtf/RefCounted.h"
 
 namespace blink {
 
 class FloatPoint;
 class ScrollableArea;
 class Scrollbar;
 
-class PLATFORM_EXPORT ScrollAnimator : public RefCounted<ScrollAnimator> {
+class PLATFORM_EXPORT ScrollAnimator {
 public:
-    static PassRefPtr<ScrollAnimator> create(ScrollableArea*);
+    static PassOwnPtr<ScrollAnimator> create(ScrollableArea*);
 
     virtual ~ScrollAnimator();
 
     // 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);
 
@@ skipping 38 matching lines @@
 
     virtual bool shouldScrollbarParticipateInHitTesting(Scrollbar*) { return true; }
 
     virtual void notifyContentAreaScrolled(const FloatSize&) { }
 
 protected:
     explicit ScrollAnimator(ScrollableArea*);
 
     virtual void notifyPositionChanged();
 
     ScrollableArea* m_scrollableArea;

[haraken, 2015/06/29 15:20:22]

Maybe can we move ScrollAnimator to the heap and use a Member for this?

[sof, 2015/06/29 15:59:41]

Keeping "platform near" objects like ScrollAnimatorMac on the heap & managing
that is the problem.

I'm not pushing for that here - there's enough complexity as it is.

     float m_currentPosX; // We avoid using a FloatPoint in order to reduce
     float m_currentPosY; // subclass code complexity.
 
 private:
     float clampScrollPosition(ScrollbarOrientation, float);
 };
 
 } // namespace blink
 
 #endif // ScrollAnimator_h