Do not greedy GC if no allocation is expected/allowed.

R=dcarney@chromium.org

Review URL: https://codereview.chromium.org/227513003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20548 ce2b1a6d-e550-0410-aec6-3dcde31c8c00