[NaCl SDK] Add exit code to ppapi_simple's PS_EXIT_MESSAGE.

R=binji@chromium.org

Review URL: https://codereview.chromium.org/69333002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@234927 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 234927