RFR: 8279642: JFR: Remove unnecessary creation of Duration and Instant objects

[Erik Gahlin]

Hi,

Could I have review of an enhancement that removes a few unnecessary allocations when consuming JFR events. It's quite common that events have no duration and there is no need to recalculate an instant twice. I also removed an unnecessary throws clause.

Testing: jdk/jdk/jfr

Thanks
Erik

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Commit messages:
 - Initial

Changes: https://git.openjdk.java.net/jdk/pull/6994/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6994&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8279642
  Stats: 10 lines in 2 files changed: 6 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6994.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6994/head:pull/6994

PR: https://git.openjdk.java.net/jdk/pull/6994