Check the input parameter returned by libcros.
Check the input parameter returned by libcros.

Libcros can return an empty string and fallback to en_US in such a case for ease of development.

BUG=chromium-os:6268
TEST=manual

Review URL: http://codereview.chromium.org/6410055

git-svn-id: http://src.chromium.org/svn/trunk/src@73602 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 081c7b17873cd3755f6697f29b27ef4a79d180ec
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