RFR: 8310574 GenShen: Should not update-references for in-place-promotions [v2]

[William Kemper]

> When a cycle _only_ promotes regions in place, it is not necessary to update refs.

William Kemper has updated the pull request incrementally with one additional commit since the last revision:

  Bring formatting up to standard

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

Changes:
  - all: https://git.openjdk.org/shenandoah/pull/291/files
  - new: https://git.openjdk.org/shenandoah/pull/291/files/2d0460e8..d69a4527

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=shenandoah&pr=291&range=01
 - incr: https://webrevs.openjdk.org/?repo=shenandoah&pr=291&range=00-01

  Stats: 15 lines in 1 file changed: 10 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/shenandoah/pull/291.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/291/head:pull/291

PR: https://git.openjdk.org/shenandoah/pull/291