Sbox IPC fix

      Second take, I had off-by-one bad check in line 164

for more info see review 3142022

BUG=52682
TEST=included


Review URL: http://codereview.chromium.org/3130037

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@56938 0039d316-1c4b-4281-b951-d872f2087c98