If constant variable is allocated in CONTEXT

Patch by Fedor Indutny <fedor.indutny@gmail.com>.

BUG=
TEST=
R=vegorov@chromium.org
Review URL: http://codereview.chromium.org/8857001

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10244 ce2b1a6d-e550-0410-aec6-3dcde31c8c00