Workaround to prevent a crash checking extensions blacklist.
Workaround to prevent a crash checking extensions blacklist.

Somehow the extensions dictionary is ending up null when we don't expect it to.
This prevents the crash but may not prevent other problems. 

BUG=29317
TEST=none


Review URL: http://codereview.chromium.org/507030

git-svn-id: http://src.chromium.org/svn/trunk/src@34808 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 45c6fcf5a50fdd5ad3e64946c852fccbdeb2ab3b
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