Refactor: Clear m_axObjectCache when AXObject detaches

Source/modules/accessibility/AXMenuListPopup.h

Index: Source/modules/accessibility/AXMenuListPopup.h
diff --git a/Source/modules/accessibility/AXMenuListPopup.h b/Source/modules/accessibility/AXMenuListPopup.h
index 16bf93ca8626ad86b3c318aab861ab7a0b204c40..58327bd501025f3f148c62573b1a2d7923f8121e 100644
--- a/Source/modules/accessibility/AXMenuListPopup.h
+++ b/Source/modules/accessibility/AXMenuListPopup.h
@@ -36,7 +36,7 @@ class HTMLElement;
 
 class AXMenuListPopup final : public AXMockObject {
 public:
-    static PassRefPtr<AXMenuListPopup> create(AXObjectCacheImpl* axObjectCache) { return adoptRef(new AXMenuListPopup(axObjectCache)); }
+    static PassRefPtr<AXMenuListPopup> create(AXObjectCacheImpl& axObjectCache) { return adoptRef(new AXMenuListPopup(axObjectCache)); }
 
     virtual bool isEnabled() const override;
     virtual bool isOffScreen() const override;
@@ -47,7 +47,7 @@ public:
     AXObject* activeChild();
 
 private:
-    explicit AXMenuListPopup(AXObjectCacheImpl*);
+    explicit AXMenuListPopup(AXObjectCacheImpl&);
 
     virtual bool isMenuListPopup() const override { return true; }