RFR: 8286392: Address possibly lossy conversions in jdk.jfr

[Erik Gahlin]

Could I have a fix of this lossy conversion issue.

Testing: jdk/jdk/jfr

Thanks
Erik

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Commit messages:
 - Initial

Changes: https://git.openjdk.java.net/jdk/pull/8600/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8600&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8286392
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8600.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8600/head:pull/8600

PR: https://git.openjdk.java.net/jdk/pull/8600