Oilpan: Prepare to move AXObjectCache to the heap

Source/modules/accessibility/AXObjectCacheImpl.h

Index: Source/modules/accessibility/AXObjectCacheImpl.h
diff --git a/Source/modules/accessibility/AXObjectCacheImpl.h b/Source/modules/accessibility/AXObjectCacheImpl.h
index ef603ea83e52558309826cf886d0f619201ab68f..4ddc39ae9f07f72bddc1587fc5861bcfbff65d45 100644
--- a/Source/modules/accessibility/AXObjectCacheImpl.h
+++ b/Source/modules/accessibility/AXObjectCacheImpl.h
@@ -55,15 +55,18 @@ struct TextMarkerData {
 
 // This class should only be used from inside the accessibility directory.
 class MODULES_EXPORT AXObjectCacheImpl : public AXObjectCache {
-    WTF_MAKE_NONCOPYABLE(AXObjectCacheImpl); WTF_MAKE_FAST_ALLOCATED(AXObjectCacheImpl);
+    WTF_MAKE_NONCOPYABLE(AXObjectCacheImpl);
 public:
-    static AXObjectCache* create(Document&);
+    static PassOwnPtrWillBeRawPtr<AXObjectCache> create(Document&);
 
     explicit AXObjectCacheImpl(Document&);
     ~AXObjectCacheImpl();
+    DECLARE_VIRTUAL_TRACE();
 
     AXObject* focusedUIElementForPage(const Page*);
 
+    virtual void dispose() override;
+
     virtual void selectionChanged(Node*) override;
     virtual void childrenChanged(Node*) override;
     virtual void childrenChanged(LayoutObject*) override;
@@ -213,6 +216,11 @@ private:
 
     HashSet<AXID> m_idsInUse;
 
+#if ENABLE(ASSERT)
+    // Verified when finalizing.
+    bool m_hasBeenDisposed;
+#endif
+
     //
     // Aria-owns
     //