Return the read only value for the given preference.
Parameters: key - the requested key the read only value throws: IllegalArgumentException - if the key is null
Update the read only value for the given key. Implementation can throw an unsupported operation exception when it
is abnormal to perform an update.
Parameters: key - the key to update Parameters: readOnly - the new read only value throws: UnsupportedOperationException - if the operation is not supported throws: IllegalArgumentException - if the key is null