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: de016e52bd170d2d4f2344f9bf92d50478b649e0@73602 0039d316-1c4b-4281-b951-d872f2087c98

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