Disable compiled_transitions by default.

This was accidently re-enabled with r15674.

TBR=danno@chromium.org

Review URL: https://codereview.chromium.org/19229003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15679 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Revert r15649 and fix for loop dominator propagation in GVN.

BUG=
R=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/19233002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15680 ce2b1a6d-e550-0410-aec6-3dcde31c8c00