Make mojo_shell work on Mac OS X again

R=darin@chromium.org

Review URL: https://codereview.chromium.org/120153003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242345 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 242345