RFR: JDK-8264987: G1: Fill BOTs for Survivor-turned-to-Old regions in full gc [v4]

[Hamlin Li]

> in JDK-8262068, we have an enhancement for full gc which will skip compacting some regions with high survivor ratio. There might be some young regions among these skipped regions. These young regions are not filled with BOTs info as they're young.
> But after full GC these young regions will become old regions, and the BOTs info is better to be filled for performance consideration.

Hamlin Li has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains four commits:

 - Merge branch 'master' into fill-bots-in-full-gc
 - refine comments, names.
 - refine the code.
 - JDK-8264987: G1: Fill BOTs for Survivor-turned-to-Old regions in full gc

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Changes: https://git.openjdk.java.net/jdk/pull/3459/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3459&range=03
  Stats: 25 lines in 2 files changed: 24 ins; 1 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3459.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3459/head:pull/3459

PR: https://git.openjdk.java.net/jdk/pull/3459