Otherwise it makes CL description like foo/bar// which is ugly.

R=vadimsh@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1468183002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@297670 0039d316-1c4b-4281-b951-d872f2087c98