fix size propery of DocumentInfo representation

Change-Id: I05ca5b105835b454593f1e3fbec682306e1bfaa2
Reviewed-on: http://review.couchbase.org/34142
Reviewed-by: Aaron Miller <apage43@ninjawhale.com>
Tested-by: Aaron Miller <apage43@ninjawhale.com>
Tested-by: buildbot <build@couchbase.com>