RFR: 8271513: support JavaThreadIteratorWithHandle replacement by new ThreadsList::Iterator

[Daniel D.Daugherty]

A trivial fix to support JavaThreadIteratorWithHandle replacement by new ThreadsList::Iterator.

-------------

Depends on: https://git.openjdk.java.net/jdk/pull/4671

Commit messages:
 - Merge branch 'pull/4671' into JDK-8271513
 - 8271513: support JavaThreadIteratorWithHandle replacement by new ThreadsList::Iterator

Changes: https://git.openjdk.java.net/jdk/pull/4948/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4948&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8271513
  Stats: 9 lines in 3 files changed: 7 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4948.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4948/head:pull/4948

PR: https://git.openjdk.java.net/jdk/pull/4948