Add -optimize-for-size flag to optimize for memory size (will be used by pre-aging CL), and remove the is_memory_constrained ResourceConstraint.

BUG=292928
R=hpayer@chromium.org

Review URL: https://codereview.chromium.org/24018009

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

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@16960 ce2b1a6d-e550-0410-aec6-3dcde31c8c00