Check if there is still time before finalizing an incremental collection.

BUG=
R=erik.corry@gmail.com, ulan@chromium.org

Review URL: https://codereview.chromium.org/629903003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24567 ce2b1a6d-e550-0410-aec6-3dcde31c8c00