Refactor: Clear m_axObjectCache when AXObject detaches

Source/modules/accessibility/AXScrollbar.h

Index: Source/modules/accessibility/AXScrollbar.h
diff --git a/Source/modules/accessibility/AXScrollbar.h b/Source/modules/accessibility/AXScrollbar.h
index a5cf88daf19f7d3366c0f35efc218749bc8103a5..847b872dcaf135c6a73ee0aabf4bc6b508095352 100644
--- a/Source/modules/accessibility/AXScrollbar.h
+++ b/Source/modules/accessibility/AXScrollbar.h
@@ -38,12 +38,12 @@ 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;