The --optimize-for-size flag should imply a small semi-space

R=hpayer@chromium.org, mstarzinger@chromium.org
BUG=

Review URL: https://codereview.chromium.org/585523002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24069 ce2b1a6d-e550-0410-aec6-3dcde31c8c00