Bandaid around a weird crasher were we end up with a NULL infobar.

      BUG=53979
TEST=None (wish I knew how to repro...)

Review URL: http://codereview.chromium.org/3341004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@58257 0039d316-1c4b-4281-b951-d872f2087c98