RFR: 8273369: Computing micros between two instants unexpectedly overflows for some cases

[Naoto Sato]

Please review the fix to the issue. Avoiding overflow by not calling nanosUntil() directly, which will overflow beyond Long.MAX_VALUE difference in nano unit.

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Commit messages:
 - 8273369: Computing micros between two instants unexpectedly overflows for some cases

Changes: https://git.openjdk.java.net/jdk/pull/5396/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5396&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8273369
  Stats: 17 lines in 2 files changed: 15 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5396.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5396/head:pull/5396

PR: https://git.openjdk.java.net/jdk/pull/5396