Add 128MB limit for executable pages.

BUG=http://code.google.com/p/v8/issues/detail?id=925
TEST=None.
TBR=jschuh@chromium.org
Review URL: http://codereview.chromium.org/4634003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5799 ce2b1a6d-e550-0410-aec6-3dcde31c8c00