Rewriting SetOwnPropertyIgnoreAttributes using the LookupIterator

BUG=
R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/468493002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23163 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Remove the extensibility flag. Instead just rely on hidden_string as indication.

BUG=
R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/466033002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23164 ce2b1a6d-e550-0410-aec6-3dcde31c8c00