[8u60] Request for Approval: 8074031: Canonicalize is-a-JS-string tests

[Attila Szegedi]

Please approve.

Bug: https://bugs.openjdk.java.net/browse/JDK-8074031
jdk9 webrev: http://cr.openjdk.java.net/~attila/8074031/webrev.00
jdk9 review thread: http://mail.openjdk.java.net/pipermail/nashorn-dev/2015-February/004230.html

Changes apply cleanly to jdk8u-dev after path reshuffling from modular source code layout.

Thanks,
  Attila.