Refactor: Clear m_axObjectCache when AXObject detaches

Source/modules/accessibility/AXScrollbar.h

 /*
  * Copyright (C) 2010 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 20 matching lines @@
 
 #include "modules/accessibility/AXMockObject.h"
 
 namespace blink {
 
 class AXObjectCacheImpl;
 class Scrollbar;
 
 class AXScrollbar final : public AXMockObject {
 public:
-    static PassRefPtr<AXScrollbar> create(Scrollbar*, AXObjectCacheImpl*);
+    static PassRefPtr<AXScrollbar> create(Scrollbar*, AXObjectCacheImpl&);
 
     Scrollbar* scrollbar() const { return m_scrollbar.get(); }
 
 private:
-    AXScrollbar(Scrollbar*, AXObjectCacheImpl*);
+    AXScrollbar(Scrollbar*, AXObjectCacheImpl&);
 
     virtual void detachFromParent() override;
 
     virtual bool canSetValueAttribute() const override { return true; }
 
     virtual bool isAXScrollbar() const override { return true; }
     virtual LayoutRect elementRect() const override;
 
     virtual AccessibilityRole roleValue() const override { return ScrollBarRole; }
     virtual AccessibilityOrientation orientation() const override;
     virtual Document* document() const override;
 
     virtual bool isEnabled() const override;
 
     // Assumes float [0..1]
     virtual void setValue(float) override;
     virtual float valueForRange() const override;
 
     // FIXME: Oilpan: turn this into a Member once the AXObject
     // hierarchy is on the heap.
     RefPtrWillBePersistent<Scrollbar> m_scrollbar;
 };
 
 DEFINE_AX_OBJECT_TYPE_CASTS(AXScrollbar, isAXScrollbar());
 
 } // namespace blink
 
 #endif // AXScrollbar_h