linux: don't crash on alert infobars.
linux: don't crash on alert infobars.

estade didn't sufficiently test his change.  Luckily, the fix is trivial.

TBR=estade

Review URL: http://codereview.chromium.org/62138

git-svn-id: http://src.chromium.org/svn/trunk/src@13334 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 19651a125c1b25ac8a5e82a258c14fb8ee6d97ab
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser