Disable locking the screen in guest sessions.
Disable locking the screen in guest sessions.

BUG=110834
TEST=Log in as guest user, push ctrl+shift+L, and nothing should happen.


Review URL: http://codereview.chromium.org/9138030

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@118498 0039d316-1c4b-4281-b951-d872f2087c98

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