RFR: 8256278: Shenandoah: Avoid num of dead callback from weak processor in Shenandoah root verifier

[Zhengyu Gu]

Shenandoah root verifier currently uses WeakProcessor to verify weak oops, but it always generates report_num_dead callback if registered. This callback fails runtime/stringtable/StringTableCleaningTest.java test with -XX:+ShenandoahVerify.

Test:

- [x] hotspot_gc_shenandoah
- [x] Passed failed test
       TEST_VM_OPTS="-XX:+UseShenandoahGC -XX:+UnlockDiagnosticVMOptions -XX:-ShenandoahVerify" make 
       CONF=linux-x86_64-server-release run-test TEST=runtime/stringtable/StringTableCleaningTest.java

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

Commit messages:
 - Avoid num of dead callback from weak processor in Shenandoah root verifier

Changes: https://git.openjdk.java.net/jdk/pull/1189/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1189&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8256278
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1189.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1189/head:pull/1189

PR: https://git.openjdk.java.net/jdk/pull/1189