Make strict_mode a flag on StoreIC.

BUG=
R=ulan@chromium.org

Review URL: https://chromiumcodereview.appspot.com/25090002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@17035 ce2b1a6d-e550-0410-aec6-3dcde31c8c00