This change means that code which is never executed is garbage collected immediately, and code which is only executed once is collected more quickly (limiting heap growth), however, code which is re-executed is  reset to the young age, thus being kept around for the same number of GC generations as currently.

BUG=280984
R=danno@chromium.org, hpayer@chromium.org

Review URL: https://codereview.chromium.org/23480031

Patch from Ross McIlroy <rmcilroy@chromium.org>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@17343 ce2b1a6d-e550-0410-aec6-3dcde31c8c00