Fix maintaining change log in push-to-trunk.

Applying the patch on ChangeLog causes local changes. To reset the ChangeLog to its original state, the "-f" option is required.

TBR=jarin@chromium.org

Review URL: https://codereview.chromium.org/201633002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19963 ce2b1a6d-e550-0410-aec6-3dcde31c8c00