Code Review Request For RT-37122: Css2Bin cannot overwrite existing writable field

[Danno Ferrin]

David, Kevin,

Please review  the proposed fix

JIRA: https://javafx-jira.kenai.com/browse/RT-37122
Webrev: http://cr.openjdk.java.net/~shemnon/RT-37122/webrev.00/

—Danno