RFR: 8372321: TestBackToBackSensitive fails intermittently after JDK-8365972

[Erik Gahlin]

Could I have a review of a PR that attempts to harden a test?

Sometimes, ClassLoaderStatistics events are dropped, probably due to a bug in the RecordingStream class when starting multiple recordings simultaneously. This is not a bug related to back-to-back chunks, so I decided to use an EventFileStream instead.

I also use TestClassLoader for verification purposes. Using PlatformClassLoader shouldn't be a problem, but it seems more prudent to have an actual object/class on the heap for the class loader that needs to be checked.

Testing: jdk/jdk/jfr

Thanks
Erik

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Commit messages:
 - Use EventStream
 - Remove empty line
 - Initial

Changes: https://git.openjdk.org/jdk/pull/29117/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29117&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8372321
  Stats: 47 lines in 1 file changed: 21 ins; 14 del; 12 mod
  Patch: https://git.openjdk.org/jdk/pull/29117.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29117/head:pull/29117

PR: https://git.openjdk.org/jdk/pull/29117