RFR: 8272609: Add string deduplication support to SerialGC

[Denghui Dong]

Hi team,

Please help review this change to add string deduplication support to SerialGC.

Thanks,
Denghui

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Commit messages:
 - fix
 - 8272609: Add string deduplication support to SerialGC

Changes: https://git.openjdk.java.net/jdk/pull/5153/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5153&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8272609
  Stats: 210 lines in 17 files changed: 208 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5153.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5153/head:pull/5153

PR: https://git.openjdk.java.net/jdk/pull/5153