Fix zone_allocator to support comparison

R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/164373008

git-svn-id: https://v8.googlecode.com/svn/trunk@19390 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Merge remote-tracking branch 'upstream/trunk' into trunk