Enable preaging of code objects when --optimize-for-size.

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: https://v8.googlecode.com/svn/branches/bleeding_edge@17343 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Fix MEMORY_SANITIZER macro redefinition error.

MEMORY_SANITIZER is defined by default in certain compiler environments (when
MemorySanitizer is enabled, of course). Do not redefine it in that case.

R=danno@chromium.org

Review URL: https://codereview.chromium.org/34503012

Patch from Evgeniy Stepanov <eugenis@chromium.org>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@17344 ce2b1a6d-e550-0410-aec6-3dcde31c8c00