Refactor ScopedAXObjectCache to remove ref count

public/web/WebAXObject.h

Index: public/web/WebAXObject.h
diff --git a/public/web/WebAXObject.h b/public/web/WebAXObject.h
index 336ed93a617bce65b18e7cbe558a1e2dffc0201d..f5c7f0f929f283e0b4d893c88f7a490cc9b2a2a2 100644
--- a/public/web/WebAXObject.h
+++ b/public/web/WebAXObject.h
@@ -32,6 +32,7 @@
 #define WebAXObject_h
 
 #include "../platform/WebCommon.h"
+#include "../platform/WebPrivateOwnPtr.h"
 #include "../platform/WebPrivatePtr.h"
 #include "../platform/WebVector.h"
 #include "WebAXEnums.h"
@@ -58,12 +59,11 @@ struct WebRect;
 class WebScopedAXContext {
 public:
     BLINK_EXPORT WebScopedAXContext(WebDocument& rootDocument);
-    BLINK_EXPORT ~WebScopedAXContext();
 
     BLINK_EXPORT WebAXObject root() const;
 
 private:
-    WebPrivatePtr<ScopedAXObjectCache> m_private;
+    WebPrivateOwnPtr<ScopedAXObjectCache> m_private;
 };
 
 // A container for passing around a reference to AXObject.