Use LookupIterator to transition to accessors

BUG=
R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/490533002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23210 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Get rid of last non-storeic use of JSReceiver::Lookup

BUG=
R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/487333002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23211 ce2b1a6d-e550-0410-aec6-3dcde31c8c00