Oilpan: move RenderObjects off heap.

Source/core/rendering/RenderScrollbar.h

 /*
  * Copyright (C) 2008, 2009 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 22 matching lines @@
 
 namespace blink {
 
 class LocalFrame;
 class Node;
 class RenderBox;
 class RenderScrollbarPart;
 class RenderStyle;
 
 class RenderScrollbar final : public Scrollbar {
-    WILL_BE_USING_PRE_FINALIZER(RenderScrollbar, destroyParts);
 public:
     static PassRefPtrWillBeRawPtr<Scrollbar> createCustomScrollbar(ScrollableArea*, ScrollbarOrientation, Node*, LocalFrame* owningFrame = 0);
     virtual ~RenderScrollbar();
 
     RenderBox* owningRenderer() const;
 
     IntRect buttonRect(ScrollbarPart);
     IntRect trackRect(int startLength, int endLength);
     IntRect trackPieceRectWithMargins(ScrollbarPart, const IntRect&);
 
@@ skipping 19 matching lines @@
 
     virtual void styleChanged() override;
 
     virtual bool isCustomScrollbar() const override { return true; }
 
     void updateScrollbarParts(bool destroy = false);
 
     PassRefPtr<RenderStyle> getScrollbarPseudoStyle(ScrollbarPart, PseudoId);
     void updateScrollbarPart(ScrollbarPart, bool destroy = false);
 
-    void destroyParts();
-
     // This Scrollbar(Widget) may outlive the DOM which created it (during tear down),
     // so we keep a reference to the Node which caused this custom scrollbar creation.
     // This will not create a reference cycle as the Widget tree is owned by our containing
     // FrameView which this Node pointer can in no way keep alive. See webkit bug 80610.
     RefPtrWillBeMember<Node> m_owner;
 
     RawPtrWillBeMember<LocalFrame> m_owningFrame;
 
-    WillBeHeapHashMap<unsigned, RawPtrWillBeMember<RenderScrollbarPart> > m_parts;
+    HashMap<unsigned, RenderScrollbarPart*> m_parts;
 };
 
 DEFINE_TYPE_CASTS(RenderScrollbar, ScrollbarThemeClient, scrollbar, scrollbar->isCustomScrollbar(), scrollbar.isCustomScrollbar());
 
 } // namespace blink
 
 #endif // RenderScrollbar_h