[NaCl SDK] Fix traceback spew from getos when Chrome is not in the path.

BUG=none
R=sbc@chromium.org

Review URL: https://codereview.chromium.org/108673002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@240147 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 240147