[8u-dev] Request for Approval: 8134502: introduce abstraction for basic NodeVisitor usage

[Attila Szegedi]

Please approve.

Bug: https://bugs.openjdk.java.net/browse/JDK-8134502
jdk9 webrev: http://cr.openjdk.java.net/~attila/8134502/webrev.jdk9
jdk9 review thread: http://mail.openjdk.java.net/pipermail/nashorn-dev/2015-September/005329.html

Changes did not appear cleanly to jdk8u-dev after path reshuffling from modular source code layout, although the changes are minimal:
- Parser API changes are omitted
- RecompilableScriptFunctionData.java Hunk #2 failed to apply solely because its context is different ("IdentityHashMap<Symbol, Boolean>” in 8 vs. "IdentityHashMap<>" in 9 on the line preceding the change).

I got the jdk8u-changes reviewed separately:

jdk8 webrev: http://cr.openjdk.java.net/~attila/8134502/webrev.jdk8u-dev
jdk9 review thread: http://mail.openjdk.java.net/pipermail/nashorn-dev/2015-September/005332.html

Thanks,
  Attila.