[8u40] review request: RT-37790: ObservableList.java is missing from javafx-src.zip

[Kevin Rushforth]

David,

Please review this simple build fix to restore some missing source files 
in javafx-src.zip in the JDK (it doesn't affect the runtime). The patch 
is in the JIRA.

https://javafx-jira.kenai.com/browse/RT-37790

-- Kevin