Put making embedded maps in optimized code weak behind a flag.

Disable the flag by default because of Chrome crashes.

BUG=172488,172489
R=mstarzinger@chromium.org

Review URL: https://chromiumcodereview.appspot.com/12091018

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@13523 ce2b1a6d-e550-0410-aec6-3dcde31c8c00