RFR: 8267894: Skip work for empty regions in G1 Full GC

[Ivan Walulya]

Hi all,

Please review this change to skip doing work on regions that were empty at the beginning of the Full GC in phases that execute on a per-region basis.

Testing: Tier 1-3.

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

Commit messages:
 - 8267894: Skip work for empty regions in G1 Full GC

Changes: https://git.openjdk.java.net/jdk/pull/5143/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5143&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8267894
  Stats: 26 lines in 5 files changed: 17 ins; 2 del; 7 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5143.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5143/head:pull/5143

PR: https://git.openjdk.java.net/jdk/pull/5143