Use std::unique_ptr instead of PassOwnPtr|OwnPtr for NamedNodeMap
https://bugs.webkit.org/show_bug.cgi?id=137201

Reviewed by Darin Adler.

No new tests, just refactoring patch.

* dom/ElementRareData.h: Use std::unique_ptr instead of OwnPtr.
(WebCore::ElementRareData::setAttributeMap): Use std::unique_ptr.
* dom/NamedNodeMap.h:
(WebCore::NamedNodeMap::create): ditto.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@174053 268f45cc-cd09-0410-ab3c-d52691b4dbfc