This mode drastically decreases pause times by limiting maximum capacity
of the young generation when mutators generate many long-lived objects.
It shrinks new space back to the initial capacity and keeps it at that
capacity until survival rate decreases again.

R=erik.corry@gmail.com

Review URL: http://codereview.chromium.org/8702006

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10072 ce2b1a6d-e550-0410-aec6-3dcde31c8c00