Add 'LOG=N' line to merge-to-branch.sh to avoid presubmit errors when merging to branch.

R=machenbach@chromium.org

Review URL: https://codereview.chromium.org/128223002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18494 ce2b1a6d-e550-0410-aec6-3dcde31c8c00