RFR: 8213177: GlobalCounter::CSContext could be an enum class

[Harold Seigel]

Please review this small change for JDK-8213177.  The change was regression tested with Mach5 tiers 1 and 2 on Linux, Windows, and Mac OS, and Mach5 tiers 3-5 on Linux x64.

Thanks, Harold

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Commit messages:
 - 8213177: GlobalCounter::CSContext could be an enum class

Changes: https://git.openjdk.java.net/jdk/pull/2895/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2895&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8213177
  Stats: 12 lines in 1 file changed: 10 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2895.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2895/head:pull/2895

PR: https://git.openjdk.java.net/jdk/pull/2895