Using "%@" will correctly requote quoted arguments. Tested with repro case.
The fix in r232184 missed the necessary argument quoting.

R=iannucci@chromium.org
BUG=314192
BUG=241769

Review URL: https://codereview.chromium.org/47873010

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@232501 0039d316-1c4b-4281-b951-d872f2087c98