RFR: 8253286: Use expand_exact() instead of expand_at() for fixed requests in G1

[Albert Mingkun Yang]

On Mon, 21 Sep 2020 07:21:45 GMT, Stefan Johansson <sjohanss at openjdk.org> wrote:

> I would like this change to only address how we expand the found regions.

Sure.

Thank you for the explanation. I think we have reached an agreement here; please update the pre-call comments and
post-call assert as discussed above. Thank you again.

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PR: https://git.openjdk.java.net/jdk/pull/235