RFR 8149929: Nashorn Parser API needs to be updated for ES6

[Sundararajan Athijegannathan]

Please review http://cr.openjdk.java.net/~sundar/8149929/webrev.00/ for
https://bugs.openjdk.java.net/browse/JDK-8149929

Nashorn Parser JEP (http://openjdk.java.net/jeps/236) added Parser API
for ECMAScript ES5.1 version. The current fix is to update the Parser
API for ECMAScript 6.

Specdiff for specification changes is here:
http://cr.openjdk.java.net/~sundar/8149929/specdiff/overview-summary.html

Thanks,

-Sundar