Refactor ScopedAXObjectCache to remove ref count

Source/core/dom/AXObjectCache.h

Index: Source/core/dom/AXObjectCache.h
diff --git a/Source/core/dom/AXObjectCache.h b/Source/core/dom/AXObjectCache.h
index 4b2d92d93330322434dafaaa717720dac2871179..e73da6b63fe417d2e13e25986925628f0763252c 100644
--- a/Source/core/dom/AXObjectCache.h
+++ b/Source/core/dom/AXObjectCache.h
@@ -43,7 +43,7 @@ class Widget;
 class CORE_EXPORT AXObjectCache {
     WTF_MAKE_NONCOPYABLE(AXObjectCache); WTF_MAKE_FAST_ALLOCATED(AXObjectCache);
 public:
-    static AXObjectCache* create(Document&);
+    static PassOwnPtr<AXObjectCache> create(Document&);
 
     static AXObject* focusedUIElementForPage(const Page*);
 
@@ -131,7 +131,7 @@ public:
     virtual const AtomicString& computedRoleForNode(Node*) = 0;
     virtual String computedNameForNode(Node*) = 0;
 
-    typedef AXObjectCache* (*AXObjectCacheCreateFunction)(Document&);
+    typedef PassOwnPtr<AXObjectCache> (*AXObjectCacheCreateFunction)(Document&);
     static void init(AXObjectCacheCreateFunction);
 
 protected:
@@ -141,19 +141,17 @@ private:
     static AXObjectCacheCreateFunction m_createFunction;
 };
 
-class CORE_EXPORT ScopedAXObjectCache : public RefCounted<ScopedAXObjectCache> {
+class CORE_EXPORT ScopedAXObjectCache {

[haraken, 2015/04/28 11:36:25]

I'm not quite sure how much this change helps Oilpan.

In Oilpan, we don't want to mix stack-allocated objects (allocated on stack) and
on-heap objects (allocated with new) for the same object type. That works fine
if you're careful but is a bit dangerous because the stack-allocated object does
not have a valid header (A disaster happens if you store the pointer to the
stack-allocated object to Member<X> and trace it). To avoid the danger, we don't
want to mix them.

Given that WebScopedAXContext needs to allocate the ScopedAXObjectCache object
on-heap, we don't want to allow stack-allocated ScopedAXObjectCache objects. So
I'd suggest making ScopedAXObjectCache NoBaseWillBeGarbageCollectedFinalized.
(In this CL, you can change ScopedAXObjectCache from RefCounted to NoBase.)

[keishi, 2015/05/28 06:49:13]

Removed stack-allocated ScopedAXObjectCache.

     WTF_MAKE_NONCOPYABLE(ScopedAXObjectCache);
 public:
     explicit ScopedAXObjectCache(Document&);
-    ~ScopedAXObjectCache();
 
     AXObjectCache* get();
     AXObjectCache* operator->();
 
 private:
-    Document& m_document;
+    OwnPtr<AXObjectCache> m_ownedCache;
     AXObjectCache* m_cache;
-    bool m_isScoped;
 };
 
 }