RFR: 8252476: as_Worker_thread() doesn't check what it intends [v2]

[Albert Mingkun Yang]

> Convert `as_Worker_thread` to non-virtual, like other `as_*_thread` methods.

Albert Mingkun Yang has updated the pull request incrementally with one additional commit since the last revision:

  review

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4167/files
  - new: https://git.openjdk.java.net/jdk/pull/4167/files/e180c729..de74ee24

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4167&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4167&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4167.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4167/head:pull/4167

PR: https://git.openjdk.java.net/jdk/pull/4167