Oilpan: Prepare moving AXObject to heap

Source/modules/accessibility/AXScrollView.h

 /*
  * Copyright (C) 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
@@ skipping 19 matching lines @@
 
 namespace blink {
 
 class AXObjectCacheImpl;
 class AXScrollbar;
 class Scrollbar;
 class FrameView;
 
 class AXScrollView final : public AXObject {
 public:
-    static PassRefPtr<AXScrollView> create(FrameView*, AXObjectCacheImpl*);
+    static PassRefPtrWillBeRawPtr<AXScrollView> create(FrameView*, AXObjectCacheImpl*);
     virtual AccessibilityRole roleValue() const override { return ScrollAreaRole; }
     FrameView* scrollView() const { return m_scrollView; }
 
     virtual ~AXScrollView();
+    DECLARE_VIRTUAL_TRACE();
     virtual void detach() override;
 
 protected:
     virtual ScrollableArea* getScrollableAreaIfScrollable() const override;
 
 private:
     AXScrollView(FrameView*, AXObjectCacheImpl*);
 
     virtual bool computeAccessibilityIsIgnored(IgnoredReasons* = nullptr) const override;
     virtual bool isAXScrollView() const override { return true; }
@@ skipping 23 matching lines @@
     // FIXME: Oilpan: Frame/ScrollView is on the heap and its
     // AXScrollView is detached&removed from the AX cache when the
     // FrameView is disposed. Which clears m_scrollView, hence this
     // bare pointer will not be stale, so the bare pointer use is safe
     // & acceptable.
     //
     // However, it would be preferable to have it be normally traced
     // as part of moving the AX objects to the heap. Temporarily using
     // a Persistent risks creating a FrameView leak, and brings no
     // real benefits overall.
-    FrameView* m_scrollView;
-    RefPtr<AXObject> m_horizontalScrollbar;
-    RefPtr<AXObject> m_verticalScrollbar;
+    RawPtrWillBeWeakMember<FrameView> m_scrollView;

[haraken, 2015/05/28 10:48:42]

Would you elaborate on why this needs to be weak?

+    RefPtrWillBeMember<AXObject> m_horizontalScrollbar;
+    RefPtrWillBeMember<AXObject> m_verticalScrollbar;
     bool m_childrenDirty;
 };
 
 DEFINE_AX_OBJECT_TYPE_CASTS(AXScrollView, isAXScrollView());
 
 } // namespace blink
 
 #endif // AXScrollView_h