bug=79427. This checkin adds the following behavior: On GetValue, if a checkbox or radio button, it returns "CHECKED" or "UNCHECKED". On SetValue, any string not equal to the empty string causes the checkbox to be set. git-svn-id: svn://10.0.0.236/trunk@96927 18797224-902f-48f8-a5cc-f745e15eee43