RFR: 8273369: Computing micros between two instants unexpectedly overflows for some cases [v5]

[Stephen Colebourne]

On Wed, 8 Sep 2021 00:36:29 GMT, Naoto Sato <naoto at openjdk.org> wrote:

>> 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.
>
> Naoto Sato has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Added comments for the test.

This change looks fine, but I think you also need a `millisUntil` private method to fix the identical overflow problem with millis (which might as well be fixed now).

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