Otherwise this creates a mess for WIP branches that do not pass the git
pre-commit hook.

R=iannucci@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1179273003

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@295742 0039d316-1c4b-4281-b951-d872f2087c98