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 e9a7813b3538b7b5d70d89cc28b03d33805e1312..697ec64dd1ffb60e60d4d4bce49243b1d15099be 100644
--- a/public/web/WebAXObject.h
+++ b/public/web/WebAXObject.h
@@ -33,6 +33,7 @@
 
 #include "../platform/WebCommon.h"
 #include "../platform/WebPoint.h"
+#include "../platform/WebPrivateOwnPtr.h"
 #include "../platform/WebPrivatePtr.h"
 #include "../platform/WebVector.h"
 #include "WebAXEnums.h"
@@ -59,12 +60,11 @@ 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.