Disable field type tracking by default.

BUG=365172
LOG=y
R=ulan@chromium.org

Review URL: https://codereview.chromium.org/247913005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20902 ce2b1a6d-e550-0410-aec6-3dcde31c8c00