Currently, any bot run with "--revision=project@origin/master" fails, because
it fetches the remote ref into refs/remotes/origin/master, but then checks out
refs/heads/master, which hasn't been rolled forward. This is very similar to
the bug fixed by https://codereview.chromium.org/85473007

However, I am very wary of this patch, because I am worried about changing
something commented with " For compatibility...". Marc-Antoine, please comment.

R=maruel@chromium.org, smut@chromium.org, stip@chromium.org

Review URL: https://codereview.chromium.org/244253007

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@266251 0039d316-1c4b-4281-b951-d872f2087c98