RFR: JDK-8234502 : Merge GenCollectedHeap and SerialHeap [v10]

[Lei Zaakjyu]

> JDK-8234502 : Merge GenCollectedHeap and SerialHeap

Lei Zaakjyu has updated the pull request with a new target base due to a merge or a rebase.

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Changes: https://git.openjdk.org/jdk/pull/16623/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16623&range=09
  Stats: 0 lines in 0 files changed: 0 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/16623.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16623/head:pull/16623

PR: https://git.openjdk.org/jdk/pull/16623