Oilpan: Prepare to move AXObjectCache to the heap

Source/web/WebAXObject.cpp

Index: Source/web/WebAXObject.cpp
diff --git a/Source/web/WebAXObject.cpp b/Source/web/WebAXObject.cpp
index 51d930305cbdedbf283cf125c9f3883ad0188fd4..ef98b5b69d6631c1ed86e7f07808f5f7b3f09631 100644
--- a/Source/web/WebAXObject.cpp
+++ b/Source/web/WebAXObject.cpp
@@ -76,13 +76,13 @@ static bool isLayoutClean(Document* document)
 #endif
 
 WebScopedAXContext::WebScopedAXContext(WebDocument& rootDocument)
-    : m_private(adoptRef(new ScopedAXObjectCache(*rootDocument.unwrap<Document>())))
+    : m_private(ScopedAXObjectCache::create(*rootDocument.unwrap<Document>()))
 {
 }
 
 WebScopedAXContext::~WebScopedAXContext()
 {
-    m_private.reset();
+    m_private.reset(0);
 }
 
 WebAXObject WebScopedAXContext::root() const