Fix NOTREACHED() in extension_prefs.cc.
Fix NOTREACHED() in extension_prefs.cc.

BUG=40017
TBR=evan@chromium.org

git-svn-id: http://src.chromium.org/svn/trunk/src@43251 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 566dceba9e1f970d5ab849982f89052c979b3e97
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