RFR: 8291753: Add JFR event for GC CPU Time [v4]

[Sangheon Kim]

> Hi all,
> 
> Could I have reviews to add new JFR event for GC CPU time?
> Currently only log message is available for CPU time (user, system, real).
> As there is already GCTraceCPUTime class which is used for a log message, I added GCTracer to deliver the event.
> The log message of CPU time is printed after GC is completed and tried to keep same.
> 
> For G1, manually checked there is not difference.
> 
> For test, I had to add an exception as GCCpuTime will be generated after GC end.
> 
> Testing: tier 1 ~ 3
> 
> Thanks,
> Sangheon

Sangheon Kim has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains five commits:

 - Merge branch 'master' into 8291753-cpu-time
 - Reflect egahlin's comment
 - Add Serial GC support and split test.
 - Split G1FullGCMark
 - Add JFR event of GCCpuTime.

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Changes: https://git.openjdk.org/jdk/pull/9760/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9760&range=03
  Stats: 225 lines in 23 files changed: 163 ins; 12 del; 50 mod
  Patch: https://git.openjdk.org/jdk/pull/9760.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9760/head:pull/9760

PR: https://git.openjdk.org/jdk/pull/9760