The previous fix wasn't broad enough: it only fixed the reference for a single Context.

Review URL: https://codereview.chromium.org/11361172
Patch from Adam Klein <adamk@chromium.org>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@12913 ce2b1a6d-e550-0410-aec6-3dcde31c8c00