Replace mapcheck dependency on HStoreNamedField with object.

R=mstarzinger@chromium.org

Review URL: https://chromiumcodereview.appspot.com/23402005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@16308 ce2b1a6d-e550-0410-aec6-3dcde31c8c00