RFR: JDK-8263495: Gather liveness info in the mark phase of G1 full gc [v7]

[Hamlin Li]

> Gather liveness info in the mark phase of G1 full gc.
> 
> Per-region liveness info in the mark phase of G1 full gc is for several purposes:
> 
> JDK-8262068 needs it to determine whether compaction of a region should be skipped
> JDK-8258431 for a JFR event that prints live set size estimate
> 
> so add this functionality.

Hamlin Li has updated the pull request incrementally with one additional commit since the last revision:

  refine names and comments, delete dead code.

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/2966/files
  - new: https://git.openjdk.java.net/jdk/pull/2966/files/7dc9751f..d24e7de4

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=2966&range=06
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=2966&range=05-06

  Stats: 20 lines in 6 files changed: 2 ins; 7 del; 11 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2966.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2966/head:pull/2966

PR: https://git.openjdk.java.net/jdk/pull/2966