RFR: 8265119: G1: update_remset_before_rebuild mixes liveness in words with liveness in bytes

[Ivan Walulya]

Hi all,

Please review this change to rename ConcurrentMark::liveness() to live_words() making it clear that this represents the number of live words between bottom and nTAMS. Adding ConcurrentMark::live_bytes() to return the same value in bytes. Additionally, I add a test for G1MixedGCLiveThresholdPercent flag.

Testing: tier 1-5.

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Commit messages:
 - Rename ConcurrentMark::liveness() to live_words(), add live_bytes and test for G1MixedGCLiveThresholdPercent

Changes: https://git.openjdk.java.net/jdk/pull/3511/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3511&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8265119
  Stats: 143 lines in 5 files changed: 135 ins; 0 del; 8 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3511.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3511/head:pull/3511

PR: https://git.openjdk.java.net/jdk/pull/3511